Negative's, just jump or get a chair, something to get you to the top of the bar. Then slowly, very slowly using as much control as you can lower yourself down, then repeat. It will help you develop the strength you need for pull ups. I don't know all this fancy science that goes with it, one of the smart folks on this forum can tell ya (Dan Kelly, Steven Low etc.) but it works. If my diet depended on my ability to cook, I would be dead right now, or crazy from eating charcoal rice or something, good luck with the culinary school I'm just gonna let the military feed me, four free meals a day, what ever I want, not burnt.