Every technical information about the DBI3 and DBT3 you can find here.
By turning the RMSS (Rotary Mode Select Switch) clockwise or counterclockwise you can set the DBI in 4 different modes:
OFF – Instrument is hard off
OP1 – Setup mode enabled
OP2 – Same as OP1 (for future use)
LOCK – Setup mode disabled
The NoSig indication in the right corner shows if the DBT3 (temperature sensor) is transmitting. When NoSig appears, the transmitter is not sending new temperature updates.