Start: Attach stirrup handles to the high pulleys of the crossover machine, grab them with a crossover grip, and stand in the middle of the station with your forearms crossed in front of your chest.
Finish: Straighten your arms so they end up about a foot outside your hips, as if your were carrying two shopping bags. Keep your upper body in the same posture throughout the movement. Pause, then return to the starting position.
When you have one weight stack instead of two, stand as shown above, but hold the handle with the arm farthest from the weight stack. Do all of your reps with that arm, then switch.