Tonar strobodisc measures the speed of your turntable. Disc has on one side 50Hz and another 60Hz, prior to using the disc investigate which side will work for you i.e. in Denmark it is 50Hz but in the US it is 60Hz. Once you remove the platter mat you place the disc over the spindle and begin with appropriate speed, then if necessary you adjust. Available speeds are: 8 1/3; 16 2/3; 33 1/3; 45; 78. Note: disc does not come with a strobe light.