More of a tip than a trick, and I’m sure others have thought of this as well, but I didn’t find anything when I Googled it, so here it is:
I’m sure we’ve all had the same thing happen; your string is the perfect length, but it’s time to change it for a fresh one. You put on the new one and tie a knot, only to find that you made it just a little bit too long or too short. Of course you can always pick the knot and retry, but that can be a pain.
Then, it dawned on me, why not just leave the old string on while I tie the knot on the new one. It’s so simple I can’t believe I never thought of it before. This is especially helpful if you use nylon string which can be a bit “bouncy” when it’s fresh.
You just leave the old string on the yoyo and put the new one on with it. Let it hang to see where to tie your knot, and voila, perfect match.