The manual my P20B came with is pretty unhelpful.
What thickness material are you trying to weld?
The spot welding copper thread has a lot of the settings I determined.
You will need some practice, even If I tell you the exact settings i used on X thickness material , as the pressure used and tip shape and distance between electrodes are all variables and will differ amongst different users.
At first, Just worry about the gear setting and use a single pulse.
A trapazoidal razor blade can help one to get the settings fairly close, before trying on real cells, and one can easily see the underside. When not enough poweris used one weld will be more prominent than the other. Go up in 20 gear increments until both welds are getting near the same size as seen from opposite side of razor, then one can play with preheating and interval and ‘intermittent’ to refine the result.