 
 <prompt> Wetin cause di revolutions? Based on di previous question, write one context wey contain di answer. E fit be 1 - 20 sentences. Context: <response>: In 1925, dem choose 78.26 rpm as di standard sake of di introduction of di electrically powered synchronous turntable motor. Dis motor dey run at 3600 rpm, so if dem use 46:1 gear ratio, e go produce 78.26 rpm. For some parts of di world wey dey use 50 Hz current, di standard na 77.92 rpm (3,000 rpm with 77:2 ratio), wey be di speed wey strobe disc with 77 lines go "stand still" for 50 Hz light (92 lines for 60 Hz). After World War II, dem come dey call dis records 78s, to separate dem from other new disc record formats. Before, dem just dey call dem records, or when dem need to separate dem from cylinders, dem go call dem disc records. 