If you bought the tt new, it should have a strobe disc-with that, you don't need a 'strobe'-a fluorescent, or even an incandescent light, held over the strobe disc, will 'flash' at 60 cycles to make the scale on the disc appear to stabilize when the speed is correct. If you don't have one, they're available at VinylEngine (free) to download and print.
Not to keep flogging this point, but until you have a way to check the actual speed of the platter, you can't make any assumptions about speed inaccuracies with your deck, or make a meaningful correction to the speed. Unless there is something horribly wrong (unlikely) your SDS will be able to produce a dead-accurate 33 1/3 (and 45) rpm.
As an aside, an idler drive is no more speed accurate, without correction, than any other type of turntable drive-the ability to hear Van Morrison farting during a recording session doesn't mean that the fart is exiting his buttockial area at the correct speed.
Not to keep flogging this point, but until you have a way to check the actual speed of the platter, you can't make any assumptions about speed inaccuracies with your deck, or make a meaningful correction to the speed. Unless there is something horribly wrong (unlikely) your SDS will be able to produce a dead-accurate 33 1/3 (and 45) rpm.
As an aside, an idler drive is no more speed accurate, without correction, than any other type of turntable drive-the ability to hear Van Morrison farting during a recording session doesn't mean that the fart is exiting his buttockial area at the correct speed.