Simulation Lab

Change something. See what happens.

Every simulation follows the same cycle: observe it, change the variables, predict what will happen, run the experiment, then read the explanation.

Validation checker

Type a value and see which validation checks it passes — then find the wrong-but-valid entry that every check lets through.

Replicate a formula down a column with and without dollar signs, and watch the tax rate silently walk off into empty cells.