So really short description, you have 33, 45, and 78 rpm.
Most record players are belt drive. Anything that is belt drive usually has some slip / variation (if more familiar to you, imagine the belt drive on a lawn tractor). Many have a finer adjustment to tune the spin rate. +- off of the selected rate. (Perhaps you selected 33 rpm but it’s really spinning at 32)
I’m sure someone who knows much more then I do, could give a much better explanation along with other types of tuning. (Arm weights, needles, etc etc)
That may be the case, my experience is with a limited number of record players.
I only commonly use a dual 1219, dual 1229, (both purchased for under $30), and a victor victrola from 1908 so my knowledge is severely limited despite having played with others it’s focused on those units.
Most record players are belt drive. Anything that is belt drive usually has some slip / variation (if more familiar to you, imagine the belt drive on a lawn tractor). Many have a finer adjustment to tune the spin rate. +- off of the selected rate. (Perhaps you selected 33 rpm but it’s really spinning at 32)
I’m sure someone who knows much more then I do, could give a much better explanation along with other types of tuning. (Arm weights, needles, etc etc)