Stanford Research Systems SR844 User Manual page 116

4-14 Gain and Time Constant
SETL(?)
SR844 RF Lock-In Amplifier
The SETL command resets the Elapsed Time counter to zero, while the SETL?
query returns the Elapsed Time as a real number, in units of the current Time
Constant, since either the last SETL command or since the Settle... key was
pressed. The SETL? query does not reset the Elapsed Time counter.