This stroboscope from Audio Technica can be used to correctly determine and adjust the speed of your turntable.

To use the Audio-Technica AT6180 Stroboscope first place the strobe on your turntable. Then, watch the strobe ring under a normal fluorescent or LED light. It should be easy to see with silver and black markings. Next, adjust the speed control of your turntable until the bands in the ring appear stationary. Your turntable is now rotating at the speed that you selected.

Four speed support: 33 1/3, 45 RPM with 50 Hz and 60 Hz markings

Dimensions: 104 mm diameter