What's the difference between a vertical climber and a stair stepper?

A true vertical climber (like the MaxiClimber) moves your arms and legs in a climbing motion against gravity or elastic resistance, while stair steppers focus on a stepping leg motion. Several listings in this category blur the line by combining stepping pedals with handlebars, and a few 3-in-1 machines add an elliptical stride, so check the motion path before buying.