The GM-1 uses infrared communication to connect itself with other GM-1 devices for synchronizing the tempo. To make two GM-1 devices play sounds with the same timing*, just set the sync settings once and then make the same tempo settings on each GM-1. This lets you make the sync settings to connect the source to each follower, each follower to each sub-follower and so on, and align the tempo settings to make the metronome sound play in time with the source device for three or more devices.
Regular metronomes only let you practice as a group if the members are within close enough range to listen to the tempo. However, with the GM-1, it does not matter whether each member is separated—just configure the sync and tempo settings to make all the devices play at the same tempo, and everyone can still practice even when they maintain an appropriate distance.
The GM-1 also features a memory backup function that automatically saves your settings from the previous use. This lets you start practicing from where you left off last time*, right when you turn on the power.
*Synchronization is canceled when the power is turned off.