Dual Stroboscope+ Protractor Disc.
Large strobe disk (dia. = 30cm = 12″), made of solid, white plastic material.
The printed strobe marks are for 33, 45 and 78 rpm, supporting 50Hz and 60Hz strobe frequency.
The back side shows a printed cartridge adjustment tool.
The null points are according Baehrwald with IEC standard for inner and outer record groove.