How do you check turntable speed?

A modern turntable has a strobe light on the side of the platter and dots embedded in the platter. When the platter is spinning, there is 1 section of the dots that should appear to remain still in the strobe light. There is one section for 50Hz electrical current, one for 60Hz, and one set fo 33.3 RPM and one for 45. If your turntable has a speed adjustment knob or slider, adjust the speed so that the proper section appears still in the light. For a belt-drive or cheaper turntable, you will have to get a reference album with specific frequency tones. Only by checking these with a tuner or computer can you see if the speed is correct. You may be able to adjust the speeds of these tables slightly, but not without taking the table apart.