Simulation controls

The bar above the workspace controls the run.

Setup: starts the world again. It runs every setup_rules, sets the tick counter to 0 and seeds the random numbers from Seed.
← Step: goes back one tick. Works from tick 1 on.
Step →: runs one tick.
Go / Pause: runs ticks until you pause.
Tick / Agents / Seed, on a wide screen: live counters. Click the seed to edit it, or click ↻ for a random one. Either runs Setup again.
Undo, on a wide screen: takes back the last change to the model's structure. That is adding, changing or deleting an agent type, rule, property and so on. Ticks and slider changes stay.

Time travel

Every Setup starts a fresh history. Running forward saves checkpoints. ← Step replays from the nearest checkpoint up to tick - 1. A change to the structure, such as a rule or an agent type, sets the model up again. That starts a fresh history too.