Hourglass Sand Timer (2D)

This 2D hourglass runs on a discrete falling-sand cellular automaton: every sand cell tries to drop straight down each step, spilling diagonally when blocked, so a stable conical pile with a natural angle of repose emerges from the grid rule alone rather than from a plugged-in slope formula. Narrow the neck and only a few columns keep an open path from the top bulb to the bottom one, throttling how many cells can cross per second; widen it and the whole neck row carries sand at once. Flip the hourglass to send the settled pile back to the top and watch the measured flow rate, elapsed time, and remaining/settled counts update live.