Grass Valley Maestro Master Control v.2.4.0 - Manual (Page 184)

MAESTRO User Manual 180
Program, Preset and AUX Buses
Warning Indicators
An indicator will appear if there is a problem with the selected source.
Non-sync Indicator
If the “NS” indicator appears on the Program LCD button, the selected
source is non-synchronous with the reference input, and cross-fades will be
disabled. However, other transition types remain available; for example, V-
fade, fade-cut, and cut-fade.
Note In order to be synchronous with the reference input, sources must be timed
within +/- 1/2 line of the reference.