There are many tools that archers have available to them that also serve coaches. One of the most useful is an arrow saw.
The reason an arrow saw is one of the most useful tools to a coach is that we often find ourselves in the position of helping archers tune their arrows. And the absolute best way to tune a new arrow is to take a tuning set of five of them (never work on a whole dozen until you have nailed down the parameters for your arrows) and test them when full length (I use bare shaft testing). (Always order your shafts and arrows uncut if you have your own saw.) They should test “weak” at full length, so then you cut a little at a time, testing as you go until they test just right. (By making small cuts and bare shaft testing them as you go, you can get a feel for how much to cut each time (each cut will move the bare shafts closer to the fletched group.) Generally the cuts get smaller and smaller as you “inch” closer to the correct cut length for your system. When you find it. Shoot the test set until you are comfortable with them and then cut the remaining arrows/shafts to that same length.
The first photo is of a Decut Minicut arrows saw which I saw an ad for at US $200. My saw is an old Apple Arrow Saw (mine doesn’t have the dust collection system like the one in the second photo), and there are modular ones that snap together, professional ones (professional arrow cutting?), etc.
Once you acquire one of these, you’ll wonder how you got along with it.