I do not know how to put numbers to the settings. My old miller has a high and a low range to plug into, also a dial with 6 settings.
When planning to weld something thin or new I will make sure to make some test welds on scrap pieces of the same thickness before
welding the final parts. There is also a wire feed speed control.

Example, for average bike frame tubes i use the low range, 5 on the dial, and adjust the wire speed until the welder welds smoothly.

On very thin steel, like the handle of a broom, almost paper thin, I use low range, 3 or 4 on the dial, and adjust the wire speed down also.

For most of my average welding, on mild steel 1/8" to 1/4" i'll use the high range, 2 on the dial, and turn the wire speed up as needed.

Experiment on scrap to find out what your welder will do at different settings.

The spool gun has it's own trigger and wire feed, with speed adjustment. It uses a different bottle of gas, argon or tri mix, and one pound
spools of welding wire.

While it does work, and lets me weld aluminum, it is one of the MOST contrary, aggravating, and tempermental tools known to man.
I have welded aluminum when at work with a better welder and it was easy. the spool gun is a pain.

what happens is after finding the correct setting for whatever is being welded, the metal being welded heats up from the welding,
and the settings are different for hot metal. So things go fine for a bit, and then , zzzzipp, the wire burns back into the tip, often kinda welding itself
inside the tip. Takes five minutes or more to take things apart, free the welding wire, clean the tip, and reassemble. Then around half of the time
the first thing that happens when starting to weld again is , zzzzipp, burn back. And so on. The other half of the time it works great.

I have been able to cut, hack, and reweld aluminum bike frames.

Steel is easier, more forgiving, and more fun.