here is my best version....
you need chin up bar...dead cheap, twelve pounds odd in any gym shop..
piece of rope or such with ( ideally ) krab at each end..
get your harness on..
clip into rope on one end and thread other end over the chin up bar and clip it to handy plastic bucket on the other side....rope should be of length that causes bucket to hang at waist height on the other side of the bar as you stand straight...like a pulley...you see..
then, place weight in the bucket to counter balance you ,, say 10 or 15kg or whatever is required to enable a one-hander..
and then crank away....
this plan is foolproof...and avoids bungee..which sucks...and is far less variable...
not that i can do a one-hander mind you...
but if i can just stop drinking god-dammit....
Cheers
damo