Set it to the same setting as the counterweight. It offsets the "push" of the outside vinyl groove so that the stylus tracks in the centre of the groove. If the phrase "setting the counterweight" is foreign to you, you should have someone set that up for you or you run the risk of ruining the stylus and your records.
I was given a Technics SL 23. I need to replace the cartridge as no replacement stylus is available. I need to know the spacing measurement for the new cartridge when I install it. Also what are these caps etc. I'm reading about. My table is fine for speed, then slows for a second or two, then is ok again. Thanks for any or all help,