Len said it.

When it happens you'll know it. You'll know then when you aren't.

I am down to just a few shafts myself and have been shooting broadheads lately. One arrow just will not fly right regardless of what I do with it, The other @ 30 will just about drill the same hole every time. You could also have a bad shaft.

I prefer goup tuning myself. Calls for putting a level line across the target and shooting some good shafts at the line from 15,20,25 yrds. Adjusting the nock hieght untill they all hit the line (then going to the next distance and doing it again). After that I do a verticle line from 20,25,30,35,40 with the same shaft adjusting the center shot until the drop right down the line using the same pin for all shots. Takes days and the weather has to be right. I do have a rest that's micro, micro adjustable. A huge help.