String meter tension vs racquetune on ipad

Which is better for getting an idea of the tension. I'm using racquetune on my ipad pro 2nd gen and it's telling me 38lbs (strung on a gamma progression 2 electric at 54lbs).

Seems low unless that's the usual baseline measurement everyone else is getting , ~ negative 10lbs ?
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I'm using racquettune in an Ipad Pro, and it's telling me surprisingly accurate results in fresh stringjobs. Typically I string various polyesters 25kg mains, 24kg crosses with my dropweight Gamma Progression II 602 FC. Racquettune reports results in between 24kg-25kg and the tension loss afterwards seems typical (drops 10%-15% during the first 2-4 hours of play and much less after that, depending on the string of course.) Very happy with racquettune and gives me all the info that I need.
Racquettune app, as well as ERT-300, measures resonance frequency of vibrations of the string bed. It works like a guitar, you pluck a string, you hear a sound, an electronic tuner tells you what note it is, and then you know if the string is tensioned weaker or stronger than needed. You want them tuned the same way each time you are going to play... Using guitar as another example, you have 6 strings with different thickness and design. If you try to tune all of them to the same note, you would have to tension them at significantly different tensions. You might not be able to pull the bass string strongly enough at all. If you install metal strings instead of nylon strings, you would need different tensions again. This example demonstrates how many factors affect what racquettune or ERT-300 measure. It also demonstrates that what you really care, is that very DT reading, not so much the actual tension which is nothing else but the means to achieve the desired DT, i.e., the desired feel of the string bed.

In theory, it might be possible to calibrate the tool and the app to exactly convert resonance frequency to tension, for a given frame, string material, string gauge, string design. In order to do it, you need to be able to maintain and measure tension of each string in a string bed for the duration of measurement. Basically, you would need a contraption with 16+19 = 35 load cells and tensioners, all pulling each string and measuring tensions simultaneously to make sure every string is exactly at the target tension, while you measure the resonance frequency. This is way too complex and way too expensive to justify the benefit - and the result will be valild only of this racquet and only for this string! All models which RacquetTune or ERT-300 use are extrapolations and approximations based on good faith assumption that if you entered 54 LBs into your machine, your string tension will be 54 Lbs on each string after you tied off and took the racquet off the machine. These models are reasonable compromises whichmay be more or less accurate depending on a specific racquet or a specific string.

2ndServe, Your question is valid, but it would make sense to describe what racquet you use and what strings you use. Results may vary depending on these factors. Only people who use the same (or at least very similar) racquet and strings may give you a meaningful answer which you are seeking.

I assume, you are taking measurements immediately after stringing and follow all instructions.
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RTFM for RT. It tells you how to derive the string factor if you are unable to measure it. It assumes that your machine is calibrated so that a pull of 50# is indeed 50#. Once you enter the correct string factor, mains, crosses, face size, you are good to go. At least for me, when I do a frame and finish, ping it etc. the tension RT gives me is my ref tension within ±0.5# max. Typically it is ±0.2#.
Stoneage is the creator of this app. Read thru his threads because this is a well behaved and developed app. You will also run across the program FREQNESS, which does indeed measure frequency, but does not calculate tension from it as well. If your RT results are suspect, then either your string factor is wrong, you are using a LO, or your stringing techniques leak tension.