Using assisted pull up machine

I was just wondering in order to use this correctly so i can improve my pull up technique, what weight should i be setting this at if i weigh around 83kgs?

to a weight you can lift yourself up for the number of reps you need to - its kind of a 'how long is apeice of string' question mate as it depends on your strength and reason for doing them ie trainign goals
 
just remember that the heavier the weight you put on the lighter it will feel when you pull yourself up so imagine your weight, less the amount of weight you have on the stack and I believe that is what you will be lifting
 
for example if you are 83kgs and you put 20 kg on the stack you wil be lifitng around 63kg

thanks