The R-ROM (regressive range of motion) method works best for bodyweight exercises where it's hard for you to get more than 12 solid reps or for which you can add some weight. Basically, it involves shorting the range of motion as you fatigue. Great for adding time under tension.

Regressive Range Of Motion Pull-Ups

1. Start by doing the full range of motion for the movement. The "easier" the exercise is for you (i.e. the more reps you can get), the slower the tempo should be. At the most, you should be getting 10-12 full-range reps with the slow tempo.
2. When you reach a point close to failure, shorten the range of motion and continue doing partial reps until failure. For pull-ups, the partials would be at the top of the range of motion.

If you want to use the method for exercises where you can normally pump out 30-plus reps – like push-ups or bodyweight squats – just start the set with a 30-second hold in the middle or bottom position, then proceed with the regressive ROM set.