Wow is it my fault that I feel like I am in a court case being interrogated sometimes on this forum? Every word that is use seem to matter suddenly, while this is a technical discussion. Please take into consideration that I am Dutch and my English is limited. Hereby some answers: If our test approximate, the test machines approximate also because their accuracy is not better than with our system. IMO you should say both measure the SW, with their own accuracy. This is exactly the same as comparing SBS testers, these show a big difference between results of different tools, because the test (with the vibration) is too complicated, including a calculation with a square in it. There has been a different discussions on forums about this one of them on the GSS forum. We have different machines in our forum team (Prince and Babolat). It also seems that the calibration with these machines give different results with the same calibration bar. This is very basic, although it was not said before, just give a player with a late backswing a racquet with a high SW and you will see what happens. Give the same racquet to a “Söderling type” and that one will not have any problem. Newton has been right for many years already. New ideas can never be found in sources. As I said, I am not in court here, we did tests in the Netherlands and someone else in Austria. I do not think that the TW calculator also advises, we did not find an advise system. The basis for the calculation is the same only from a different point moved to the pivot point. This is the basis for the SW machines! So these machines have to use this forumula to get from swing-time to swingweight. And because the square is the first reason for the low accuracy. Could it also be that Head found out that this is quite a good way to test the SW of their racquet? Head would not be able to pay 2000 dollars for the Prince machine? Common!