Read the notes and credits. tl;dr: If you want highly accurate and highly precise actions in scratch, multiply any repeated action by the time delta since the last time the action occurred rather than just using a wait block.
Both cats are trying to move at 10 steps per second. The top cat uses a forever loop where it waits 0.1 seconds, moves one step, and repeats. The bottom cat uses a time delta step speed. It loops as fast as it can, and moves by a number of steps equal to 10 times the amount of time that passed since the last step. After 15 seconds, a percentage error for each cat is calculated. As you can see, the timer cat's speed (bottom) is significantly more precise and accurate than the wait cat's speed (top).
