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TW Staff
04-21-2008, 12:26 PM
Check out the new Tennis Warehouse University.

Brush up on your racquetology and string theory:

http://twu.tennis-warehouse.com/learning_center/contents.html


You guys are the first to see this. Please post feedback here and let us know if you find any broken links, have questions or any other issues.

We hope you enjoy it.

Thanks,
Chris.

Bronc10is
04-21-2008, 12:30 PM
just quickly browsed through it, awesome feature. Thank you TW

Ferrari1190
04-21-2008, 12:31 PM
awsesome, it has all the info you'd ever need!
thanks :)

Nitro
04-21-2008, 12:33 PM
Great idea. Very interesting to read.

lude popper
04-21-2008, 01:17 PM
FINALLY

I've been waiting for years for the industry to update their tired power formula. This replaces an abstract formula with something empirical. Rather than applying one non-desrcript power reference to the entire stringbed, this gives us a functional, detailed power grid. It answers the how, why, when, and where of power -- and it gives us the actual data along with an easy-to-understand interpretation. Power de-mythologized. You have opened up a very large door here. Kudos.

babolat15
04-21-2008, 01:50 PM
this is incredible, just wondering is 3 percent going to make that huge of a difference

VGP
04-21-2008, 01:52 PM
Thanks.

I hope it's well received.

Chauvalito
04-21-2008, 02:04 PM
TW, at some point can you post the methods used to calculate the power potential?

I apologize if it is already posted, I looked through the site quickly. Very cool.

todd03blown
04-21-2008, 02:16 PM
very cool indeed!!

meowmix
04-21-2008, 05:12 PM
SWEET!!!

You DEFINATELY need to put more stuff in the Nerds category to make us feel special :)

Wow, I never knew that the microgel prestige mid was so powerful... more so than my Gamma!!!

TW Staff
04-21-2008, 05:31 PM
Please play around with some of the features and let us know if anything is not working or needs further explanation.

Thanks for everyone's feedback.

Cheers,
Chris.

MAX PLY
04-21-2008, 05:42 PM
Very nice feature. Thanks for thinking of it and executing it.

bertrevert
04-21-2008, 05:53 PM
Racquet choice - swingweight THE MOST important factor!
http://twu.tennis-warehouse.com/learning_center/totalperformance.html

I thunderstruck. So many of the threads in the racquet's forum needed to be more about swingweight - that great intangible. Sure it's measurable, but only in matchplay do you find out how much you personally can keep swinging (to the end of the match).

Great stuff, v. interesting.

Lots of homework at this uni... you're introducing a lot of new ways to discuss racquets. Thank you.

PS. I like the fact that the sweetest spot is the 'G' spot... :P

bertrevert
04-21-2008, 05:54 PM
link missing on:
http://twu.tennis-warehouse.com/learning_center/totalperformance.html

here:
" click here to look up TW's measured value or click here to use the TW Online Swingweight Machine to measure..."

Soundog
04-21-2008, 07:52 PM
Wow ! Thanks TW for a very thorough and well explained run-through of raquet performance parameters in a common sense, no nonsense presentation.

Perhaps for future addition - a similar thing for strings ? I would like to see graphs of tension ( kgs and pounds ) vs elongation ( mm ) of different strings right up to the point the string snaps given a standard length of string ( say 30cm or so ). This will allow stringers to know at what tension a string will snap and will give us an idea of how a string will behave at different tensions.

Also how flexible a string is might be useful.

For the ultra nerds, if the measurements are for various standard string lengths say 5cm, 10cm and 30cm, then it will further help us guess behaviour over various frame sizes as well. ( 5cm measurements to represent very off-centre hits close to the frame. )

And for us incurable nerds, weights of strings in terms of grams per cm ( or some other suitable measure ) could be useful as some thick poly stringbeds can weigh a few grams more than a thin kevlar string for example. I've found that when trying to hit a 50gm ball on to a 3 inch line from a distance of 78 feet, a few grams has an effect and complements the weighting of the frame.

Perhaps even friction measurements of different strings by dragging a ball with a weight on top over a string bed and measuring the force required to move the ball over the string bed graphed verses different weights on top of the ball.

That should take the guesswork and mystique of out string selection !

:mrgreen:

eagle
04-21-2008, 08:07 PM
Super!!!

r,
eagle

TokyopunK
04-21-2008, 08:10 PM
link missing on:
http://twu.tennis-warehouse.com/learning_center/totalperformance.html

here:
" click here to look up TW's measured value or click here to use the TW Online Swingweight Machine to measure..."

and also "the fastest shots do not come from the locations of maximum power (click here for explanation)."

LanEvo
04-21-2008, 09:23 PM
this is a great site thx tw

Ryoma Kun
04-21-2008, 09:31 PM
great site, i learned something!

jorel
04-22-2008, 07:40 AM
will there be a Master's degree?... i think i have my bachelors already

jorel
04-22-2008, 07:59 AM
Please play around with some of the features and let us know if anything is not working or needs further explanation.
Thanks for everyone's feedback.

Cheers,
Chris.

I love the power imbalance article and never realized that a racquet can be unbalanced lengthwise... it definitely needs more pics to indicate your point and to teach us how to determine if our racquet is unbalanced...

i would also like to suggest that (if the task is not too herculean) to have certain racquets power imbalance measured (maybe not for every racquet) but maybe for every racquet that a review is written for the racquet. it would be nice to know which racquets are the most balanced. (most well made?)


thanks... great stuff!

TW Staff
04-22-2008, 09:25 AM
Thanks for the continued feedback. We will get the links fixed.

Jorel,
We tested tons of racquets for power imbalance, but it only gave the imbalance of each specific racquet and may not be indicative of all such racquets that are the same model.

I think the important issue is, if you want to match your racquets perfectly, you have to consider the imbalance from side to side as well as the weight, balance and swingweight etc.

Chris, TW.

Soundbyte
04-22-2008, 09:32 AM
There's a typo on the ComparePower site:

"Power Potential: At each location the ball will rebound off the racquet at the indicated percentage of its impact speeed. For more discussion on what the numbers mean:"

fantom
04-22-2008, 09:49 AM
Prince O3 Speedport Tour picture is not working while using the "Compare Racquet Power Levels" application.

tzinc
04-22-2008, 09:54 AM
This looks awesome. But from a quick look it looks like you have some racquets missing like the APDC.

Kaptain Karl
04-22-2008, 09:59 AM
I am intrigued. After Girls Season is finished (two weeks) I'll spend more time studying this resource. I think I like it....

In the "Maximum Shot Speed" link, I'm pretty sure something is written backwards.

Ingredient Two Revised: Location Speed

Second, the speed of the racquet is not the same at each point on the racquet. As you move from butt to tip, the speed gets faster and faster. That's because the racquet swings in a giant circle and points in the center of the circle travel in smaller circles than those near the tip, but in the same amount of time (i.e., faster). Those "points in the center of the circle" are not moving faster; they are moving slower. They just cover a smaller arc (less distance).

Am I reading this wrong?

- KK

TW Professor
04-22-2008, 10:05 AM
I love the power imbalance article and never realized that a racquet can be unbalanced lengthwise... it definitely needs more pics to indicate your point and to teach us how to determine if our racquet is unbalanced...



Jorel: We should have a least one pic up soon. Balancing a racquet along the long axis is not easy. However, we have a very good method of doing it, as you will see in the pic.

We discovered the side to side imbalance when we noticed many racquets have more power on one side than the other. The most logical conclusion was that one side had more weight and that the weight was distributed to increase the power at a given location on the imbalanced side. Balancing along the long axis proved this to be true most of the time, but not all the time. Power imbalance can also arise from unequal side-to-side stringing, unequal flex or torsional stiffness among other things and these won't show up as unbalance from left to right.

But as Chris said, the main thing to realize is that a perfectly balanced and customized racquet will also take longitudinal balance into account.

TW Professor
04-22-2008, 10:11 AM
This looks awesome. But from a quick look it looks like you have some racquets missing like the APDC.

Yes, some racquets are missing. We have about 200 racquets tested. Some of the newer ones remain to be tested and we will fill in the older ones as we go.

Only current racquets (or closed out models for which TW has inventory) will be linked for reviews, prices, purchase, etc. However, we will retain data on older racquets so you can compare your discontinued sticks with current ones.

GPB
04-22-2008, 10:18 AM
This info is pretty awesome, and really simplifies things. I can't wait to see it finalized.

tzinc
04-22-2008, 10:19 AM
Yes, some racquets are missing. We have about 200 racquets tested. Some of the newer ones remain to be tested and we will fill in the older ones as we go.

Only current racquets (or closed out models for which TW has inventory) will be linked for reviews, prices, purchase, etc. However, we will retain data on older racquets so you can compare your discontinued sticks with current ones.

That's great since a lot of people use older sticks and will be using them for some time since they stock up or continue hunting them down. This University looks like it could take up a lot of my time and probably other people's too studying there lol.

Rabbit
04-22-2008, 10:21 AM
This is great. I will definitely spend more time on it. Keep up the innovative work, TW.

TW Professor
04-22-2008, 10:54 AM
I am intrigued. After Girls Season is finished (two weeks) I'll spend more time studying this resource. I think I like it....

In the "Maximum Shot Speed" link, I'm pretty sure something is written backwards.

Ingredient Two Revised: Location Speed

Second, the speed of the racquet is not the same at each point on the racquet. As you move from butt to tip, the speed gets faster and faster. That's because the racquet swings in a giant circle and points in the center of the circle travel in smaller circles than those near the tip, but in the same amount of time (i.e., faster). Those "points in the center of the circle" are not moving faster; they are moving slower. They just cover a smaller arc (less distance).

Am I reading this wrong?

- KK

Perhaps a bit confusing. I hope the edit (done) is better (but, alas, longer).

TW Professor
04-22-2008, 11:00 AM
This University looks like it could take up a lot of my time and probably other people's too studying there lol.

This is just the tip of the iceberg. We intend to keep expanding it.

vkartikv
04-22-2008, 11:25 AM
I'd really like to see how some of the older racquets fare... The 6.0 85/95 and 6.1 classic would be some of those..

FH2FH
04-22-2008, 11:42 AM
Very cool idea. Lots of good info, but it gets a little wordy. I think the University should be more concise [fewer pages/links] and have more graphics. Waiting for the Cliff Notes version... ;)

sonicboi21
04-22-2008, 12:34 PM
I think you are missing some importany sticks a lot of ppl use. like APDC.

Serpententacle
04-22-2008, 02:51 PM
I think you are missing some importany sticks a lot of ppl use. like APDC.

I agree. There's the APDC+, but not standard. Why is this? Most people own the standard.

TW Professor
04-22-2008, 03:27 PM
I love the power imbalance article and never realized that a racquet can be unbalanced lengthwise... it definitely needs more pics to indicate your point and to teach us how to determine if our racquet is unbalanced...



Photo now up on http://twu.tennis-warehouse.com/learning_center/powerbalance.html

jorel
04-23-2008, 05:24 AM
Photo now up on http://twu.tennis-warehouse.com/learning_center/powerbalance.html

do you have a pic of how to balance the racquet lengthwise?

Lee James
04-23-2008, 05:29 AM
looks good!

TW Professor
04-23-2008, 06:15 AM
do you have a pic of how to balance the racquet lengthwise?

Jorel, you probably have to refresh your page. The picture of lengthwise balance is up.

jorel
04-23-2008, 06:38 AM
Jorel, you probably have to refresh your page. The picture of lengthwise balance is up.

nice...........

jorel
04-23-2008, 06:44 AM
Thanks for the continued feedback. We will get the links fixed.

Jorel,
We tested tons of racquets for power imbalance, but it only gave the imbalance of each specific racquet and may not be indicative of all such racquets that are the same model.

I think the important issue is, if you want to match your racquets perfectly, you have to consider the imbalance from side to side as well as the weight, balance and swingweight etc.

Chris, TW.

so I am assuming now that if we order a racquet from TW and ask for a racquet to be balanced from side to side for us.... it can be done for us?

if so,..... THATS AMAZING SERVICE (in line with the service that many of the top racquet builders in the world give to the pros)

Gee
04-28-2008, 04:33 AM
As I viewed TW University I noticed that not all frames are available in the database. For example Head MG Prestige MP is not mentioned. Why is this?

Gimmick
04-28-2008, 07:57 AM
This tool has some nice comparative uses, but it could break down into a useless pile of crap if used improperly. For example, if you go to location "c" and look up the Flexpoint prestige team MP, you will find that its two closest stable mates are the Kinetic Pro 5g and the Metallix 2.
If "c" is your happy spot and you decide to demo these three 'nearly identical' racquets you will be sorely disappointed to find how completely different they are and how useless "power potential" was to your search.

If however, you already know what swingweight, balance, and weight range you are looking for, using power potential to check sweetspots and chartacteristics could be extraordinarily beneficial.

In summary, caveat emptor.

TW Professor
04-28-2008, 07:59 AM
We simply have not tested all the racquets yet. They will come on line as we get them done.

TW Professor
04-28-2008, 08:40 AM
IThis tool has some nice comparative uses, but it could break down into a useless pile of crap if used improperly. For example, if you go to location "c" and look up the Flexpoint prestige team MP, you will find that its two closest stable mates are the Kinetic Pro 5g and the Metallix 2.
If "c" is your happy spot and you decide to demo these three 'nearly identical' racquets you will be sorely disappointed to find how completely different they are and how useless "power potential" was to your search.

If however, you already know what swingweight, balance, and weight range you are looking for, using power potential to check sweetspots and chartacteristics could be extraordinarily beneficial.

In summary, caveat emptor.

Yes, caveat emptor to everything. And yes everything is relative to the "experience" of the racquet. But, what power potential has told you is this: if you want a racquet with x amount of power, then these are your choices, so demo them and see which one you like. If you don't like any of them, then you will have to settle for racquets that deliver more or less power than what you were looking for. Choose the "next best" power range and demo again.

Power potential tells you about the performance of the racquet, not about the player's happy or sad experience with that performance level. If a player gets more ball velocity, depth, or spin from a racquet with a lower power potential, that means that the PLAYER is doing something with the racquet to deliver those results, like swinging faster or at a different angle. Power potential is a measurement of the racquet performance. It is scientifically correct to say one racquet is or is not more powerful than another. This statement in turn does not mean that the player will or will not interact with the racquet to get more or less power (or control or comfort) while playing.

When you pick a racquet off the shelf it is what it is. Power potential lets you know what, in those now famous words, "is, is." But further, power potential is the only measurement that tells you what the racquet does. It is an actual measurement of performance. All a racquet does is rebound a ball. Power potential tells you how well it does its job. It doesn't tell you how much you will like how it does its job. That's why there are 200 racquets out there.

jorel
04-29-2008, 06:17 AM
I

Yes, caveat emptor to everything. And yes everything is relative to the "experience" of the racquet. But, what power potential has told you is this: if you want a racquet with x amount of power, then these are your choices, so demo them and see which one you like. If you don't like any of them, then you will have to settle for racquets that deliver more or less power than what you were looking for. Choose the "next best" power range and demo again.

Power potential tells you about the performance of the racquet, not about the player's happy or sad experience with that performance level. If a player gets more ball velocity, depth, or spin from a racquet with a lower power potential, that means that the PLAYER is doing something with the racquet to deliver those results, like swinging faster or at a different angle. Power potential is a measurement of the racquet performance. It is scientifically correct to say one racquet is or is not more powerful than another. This statement in turn does not mean that the player will or will not interact with the racquet to get more or less power (or control or comfort) while playing.

When you pick a racquet off the shelf it is what it is. Power potential lets you know what, in those now famous words, "is, is." But further, power potential is the only measurement that tells you what the racquet does. It is an actual measurement of performance. All a racquet does is rebound a ball. Power potential tells you how well it does its job. It doesn't tell you how much you will like how it does its job. That's why there are 200 racquets out there.

What is your superhero identity? TW Prof

jazar
04-29-2008, 06:51 AM
looks amazing

ufg8r
05-01-2008, 03:41 PM
I'm really impressed.

ndtennis
05-01-2008, 04:04 PM
great idea

jorel
05-02-2008, 12:29 PM
why no map for the Donnay Pro One MP?

matchmaker
05-04-2008, 08:51 AM
Same request as above: put the Donnay Pro One Int'l MP in the database and while you are at it the PK Redondo's also. If you want us to be able to compare any racquet to any other they all should be in the database, if not the tool becomes rather useless.

harry2110
05-05-2008, 07:22 AM
awesome page love the amount of information you provide

dman72
05-06-2008, 12:02 PM
According to this calculator, the Dunlop m-fill 400 is less powerful than a prince 03 tour mid....from my experience this is no way true.

Still, awesome feature. Maybe it has some bugs?

ClubHoUno
05-06-2008, 09:53 PM
Nice feature - thanks for that :D

Mark Vessels
05-12-2008, 01:53 PM
Is there any scholarships?

What are the requirements to be accepted?

jace112
05-13-2008, 06:36 AM
Thanks for this powerful toy :)

I have few questions:

How do really you measure the power potential? I understand that the racquet is swung at a determined speed, the ball launched at a determined velocity and then you measure the final ball velocity after the rebound. Right? But how you do that in practice? You have some robot doing the job? How is the racquet fixed?

I think you should also warn people about the swingweight. Of course it can dramatically increase power potential, but only if you're strong enough to swing the racquet fast enough.

I've played with Speedport for the last weeks, and many of my friends who tested it find it really difficult to swing and couldn't handle the SW.

The "plus or minus 10 percent of the swingweight of your current racquet " is bit too large IMHO. 5% should do the job.

About confort: I also agree in some parts with your explainations (power = confort), but maybe vibrations should also be considered. A stiff (=powerful) frame can generate bad vibrations (higher frequencies) and feel not very comfortable. A bending and twisting frame such as the old Head Radical TT OS feels very comfortable, specially on off centers near the tip.

THANKS again for your university!

Pete Semper
05-14-2008, 05:57 AM
why no map for the Donnay Pro One MP?

Same here...Please add the Donnay Pro One Int in your list. I need to compare it with some others frames.

TW Professor
05-14-2008, 09:41 AM
Thanks for this powerful toy :)

How do really you measure the power potential? I understand that the racquet is swung at a determined speed, the ball launched at a determined velocity and then you measure the final ball velocity after the rebound. Right? But how you do that in practice? You have some robot doing the job? How is the racquet fixed?



The test method is described on the following page:

http://twu.tennis-warehouse.com/learning_center/test_method.html

ej
05-22-2008, 09:41 PM
According to this calculator, the Dunlop m-fill 400 is less powerful than a prince 03 tour mid....from my experience this is no way true.

Still, awesome feature. Maybe it has some bugs?

Are you swinging these frames at the same speed?

Rebound potential is a static fact about the racquet, but the power you get from it is not. A 17 ounce frame with a 600 swingweight has more power than a 11 ounce frame with a 315 swingweight. However, you might get more power from the 315 (because you can swing it that much faster). Does this mean that the 315 has more power? No. Why? Because the tool is not meant to describe your power potential. It's meant to describe something in the racquet, like swingweight or balance. The point is to give you information about the racquet. Translating the specs into your game is part of the fun. Now... at least you have the tools. This is a good thing.

TW Staff
05-26-2008, 03:22 PM
How To Measure Your Racquet's Swingweight

http://twu.tennis-warehouse.com/learning_center/howto_swingweight.html

Chris, TW

TW Staff
05-26-2008, 03:23 PM
Also a very easy way to measure your racquet's balance at the bottom of that page.

All thanks to the TW Professor.

Chris, TW

jace112
05-27-2008, 04:11 AM
THANKS a lot

jorel
05-27-2008, 05:10 AM
Also a very easy way to measure your racquet's balance at the bottom of that page.

All thanks to the TW Professor.

Chris, TW

a question...

wont that balance technique be different for different length racquets... seems like that technique will only work for Std. length racquets

Koz
05-27-2008, 04:49 PM
While this information is very interesting and useful to read, I can't help but get the impression that there are way too many people here who worry more about the minutia of their racquet specs than their overall tennis skills and how they can improve.

Being a weekend warrior tennis pro at a YMCA, as well as having a job as a mechanical engineer, I think I get a decent exposure to both aspects. I love to know the geeky stuff, but at the end of the day, you're not going to lose a match because your racquet is .04 ounces off balance. You're going to lose it because the other person played better/smarter than you, and not because their racquet had a swing weight of 322 instead of 320.

That being said, kudos to TW for the awesome work on this! I only briefly skimmed the main page, but it looks very interesting! Remember guys, tennis is very much a mental game. I see too many people psych themselves out and think that if they added a tiny bit of lead they'd be worlds better than they are. News flash...it doesn't work that way. Just go out there, play, and have fun.

jace112
05-27-2008, 11:01 PM
a question...
wont that balance technique be different for different length racquets... seems like that technique will only work for Std. length racquets
No, simply because you don't measure HL or HH balance here. Just the balance from the butt, in cm. It doesn't matter if your frame is XL or not.

jorel
05-28-2008, 09:45 AM
No, simply because you don't measure HL or HH balance here. Just the balance from the butt, in cm. It doesn't matter if your frame is XL or not.

so its not like your using this measurement to measure points of head lightness but its purely a measure in cm....

jace112
05-28-2008, 09:46 AM
so its not like your using this measurement to measure points of head lightness but its purely a measure in cm....
exactly :)

backhand
06-11-2008, 09:34 AM
Hello all: Been away from the game, and mostly from here, for a couple of years. Injuries. Come back to buy a stick, discover TWU, excellent idea, nicely constructed, seriously addictive. But that said, there's still an obvious problem that TW has never addressed in its reviews, and again seems ready to dodge: wild inconsistency between different "official" measures of how a racquet performs.

Take the Yonex RDS 003 and RQiS 1 Tour. Really different sticks, right? TW's own player review emphasizes how low powered the RQiS is, while TW's capsule player review of the 003 - and every post or comparative review on this site - seem to agree that it's a nice blend of power and control, a "tweener."

Wrong. According to TWU numbers and my SPSS program, there is NO statistically significant difference between the power ratings at 13 sites for the two racquets. Huh?

Or take the Kblade Tour. TW's review gives it a remarkable 76 rating for power. (You can compare this to a 77 given the Prince Speedport Red, which is considered an easy tweener verging on game control.) Yet the TWU 13 site power numbers put it at the same level, statistically speaking, as a Yonex RDS 001 mid, which was rated at 63 in its TW review.

Now two or three years ago we were resigned to this kind of non-replicability in the written reviews, as well as "grade inflation" over time. After all, they're purely subjective. But if we are to believe these TWU numbers (and I do), then it would be very helpful if you TW folks took on the glaring lack of agreement with and among your own reviews UP FRONT instead of the usual "your mileage may vary, go demo." WHY do you think that you're producing this kind of disagreement between empirical and subjective reviews? Looking into it might even teach all of us more about why racquets play as they do.

So yes, TWU's a superior feature, and yes I for one am very grateful to have anything this rigorous and fun offered, let alone for free, and yes, it will predispose me to buy more stuff from you. But having set it up, why not take a deep breath and tackle the obvious issues it raises?

Josherer
06-19-2008, 03:31 AM
Great Work TW

:)

certifiedjatt
06-21-2008, 09:48 AM
"graphs for nerds."
hahaha

educational, AND fun.

gcfalcon09
07-26-2008, 07:57 PM
sweet!! works awesome!

madmanfool
07-27-2008, 03:12 AM
thanks, now i finally know the swingweight of my racquets.
One comes at 368, the other at 380. Great!

SunDog
09-02-2008, 12:23 PM
I don't understand why time to complete ten swings is an input for swing weight. The units for SW are mass x distance x distance. There is no time component in the resulting units.

If you had two racquets with the same lenth, balance point and mass - would you not expect the swing weight to be the same? If not - then what would you adjust to make it the same without changing the mass or balance point of either?

jace112
09-02-2008, 03:46 PM
I don't understand why time to complete ten swings is an input for swing weight. The units for SW are mass x distance x distance. There is no time component in the resulting units.

If you had two racquets with the same lenth, balance point and mass - would you not expect the swing weight to be the same? If not - then what would you adjust to make it the same without changing the mass or balance point of either?
It's all about polarization :)

JT_Productions
09-02-2008, 08:59 PM
Very nice!

TW Professor
09-03-2008, 07:00 AM
I don't understand why time to complete ten swings is an input for swing weight. The units for SW are mass x distance x distance. There is no time component in the resulting units.

If you had two racquets with the same lenth, balance point and mass - would you not expect the swing weight to be the same? If not - then what would you adjust to make it the same without changing the mass or balance point of either?

There are many equivalent formulas for arriving at physical properties. SW=M x d x d is just one, just as energy has E=mc^2, E=Fd, E=.5mv^2, etc. You use whatever parameters you have available to you to derive the property of interest.

You can use M x d x d to determine how much swingweight will be added to a racquet by adding lead tape to a discrete, localized spot on the racquet. However, it is meaningless to use it for the racquet as a whole because each atom of weight is located in a different position.

Pendulum method: the period of a pendulum depends only on length. Longer lengths have longer periods. But that is for a localized mass on a string (a bob). A racquet swinging as a pendulum has mass distributed all over (I guess you can imagine each atom of the racquet as a separate pendulum, each with a different period if they weren't connected to each other). The period of the racquet essentially tells you the effective length of the "racquet pendulum" as if it were a simple bob pendulum, and this depends on how all the mass is distributed and that is related to swingweight. The relationship can be expressed by a formula from which swingweight can be calculated.

An RDC works on the same principle. Instead of gravity as the driving force, a spring is used. Springs too are simple harmonic pendulums with constant periods depending on stiffness. So, the RDC will use the swing time to calculate swingweight.

As to your question of equal weight, balance and length of racquets having the same swingweight--this can be true but certainly is not necessarily true. You can distribute all kinds of crazy ways with all kinds of swingweights and end up with the same wt, bal. The best way to see that is to go to the TW University Customizer and play around with different combinations:

http://twu.tennis-warehouse.com/learning_center/customization.html