The term Knots" came from boats that would drop a rope in the water tied to a small log or something, they could watch the rope run out and it was marked by a knot every so far, they would then count the knots to determine the ship's speed. I found a super heavy duty wind up clock that makes a contact at time intervals, it would be hooked to some sort of sensor, to measure speed.
How about marking your table with chalk like you use on a blackboard if you want distances. i sometimes think I might learn a bit by placing mirrors against rails and using one of those laser pens to show reflection, not something you'd do in play bit maybe just to recognize patterns better? how do I hit from here to do 3 banks side, for example. buying a tape measure doens't sound like an issue. I dont believe in Ghosts.
Laser pens are banned.
Try conical lighting, there is more noise to work through. Its tough to isolate ghosts, there should be a ghostsink.
how would someone ground a signal in a water bubble?