an instrument for determining the difference in phase between two related motions, as those of two aircraft engines or two electric generators.
Origin of synchroscope
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
an instrument used to indicate whether two periodic quantities or motions are synchronous
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012