Just keep the jag really tight on the rod and a piece of tape with a mark on it on the rod to watch the rotation. It can get dicey because you usually only get a 1/4 turn.
Twist rates aren't odd ball and assorted, it's either going to be one or the other and we can only get a close idea with this measurement.
1-48 you'll see a 1/4 turn in 12", a 1-60 a 1/4 turn in 15". Some guy's get weird and confused when they see a 1/4 turn in 14 1/4",,"I have a 1-57' twist" :youcrazy: