Adjust tower unit and ensure cross bar is in front position. Stand on top step and grip cross bar shoulder width apart in the underhand position. Slowly lower body until arms are fully extended. Your knees are bent. Slowly pull yourself back up to starting position and hold position briefly. Repeat until a full movement is no longer possible.

Negative version:
Just do the first part of the exercise, i.e. lower body into extended position. This movement should take about ten seconds. Then climb back up and repeat until a full movement is no longer possible.
You can increase the load further by using the belt.

Important: Do not swing or thrash about. Your hip remains straight.