The two-rope latch that can also do the counting
In the theatre workshop, I tested a little pulley rig with two thin ropes. Pull one and the belt barely twitches. Pull both the same way and a latch snaps, and a painted mark ends up left or right, staying put when I let go.
The older rig needed a chunky relay box nearby to pass the shove across and help with checking. It took up space and hated vibration, so a stray knock could muddle things. Pack loads of rigs close together and that extra box becomes the problem.
The new rig bins the relay box. The two ropes run straight to the latch, one from a row line and one from a column line. Only the combined pull at that one point can flip it. Pull just one rope, or pull against each other, and nothing gives.
Reading the mark uses a second loop and a gentle test tug. It makes the indicator ready to click, but too weak to shove the belt itself. Depending on which way the belt is set, one tiny gate clicks first and sends a small signal down a shared line.
Then we set lots of identical rigs in a grid. A row pull primes a whole line, then a column pull picks the one station where both pulls meet, so only that latch snaps. When we check them one by one, we sometimes have to pause so the shared line stops wobbling.
The odd bit is what happens when we check several stations in one column at once. Each station set to the same choice gives the shared line a small tug, and the tugs add together. The counter at the end can register a total, not just a yes or no.
With the old relay boxes, the floor filled up with bulky parts that needed careful handling. With direct row and column pulls, each latch can sit quietly without a steady shove, and the same shared line that reads the choices can also add them up.