ZUMA is a classic interval workout: 40 seconds of work followed by 20 seconds of rest, repeated 10 times. Each round of consists of 3 exercises (Squats, Burpees, and Sit Ups) that each last 40 seconds followed by 20 seconds of rest. To measure your performance, count your reps per round. The goal is to keep your reps count as constant as possible for the duration of the entire workout.
Scaling: You can scale ZUMA by decreasing the working times from 40 to 20 seconds.