I'm aware that there is a test one can do to see if a shuttle is slow or fast...An underarm forehand shot from the back But what if you get stronger or weaker, or something goes in technique.. e.g. your arm was a bit close to your body. Or you hit the shuttle higher than normal. Or what if you swung harder than normal.. maybe you were more relaxed and thus hit it harder. Or more relaxed and thus didn't hit it as hard. Or were too tense and hit it less hard. Or if you cut it a little bit and it didn't go so straight. Let's say that to do the test, you have to get good at hitting a correct speed shuttle, at the right strength and with the right technique, such that standing behind the rear service line it goes to the back tramlines.. Well, let's say you do it for that shuttle, but how do you know it was a correct speed shuttle? Similarly, if I am playing a game, a clear may send the shuttle perfectly into the middle of the back tramlines, Then in another game, for whatever reason, a clear doesn't. I don't know if the shuttle was slow or if it's a flaw in technique. One could use that method of testing a shuttle, before the game starts. But then that method seems to have the issue mentioned above.