Setup the LGSW for daytime activity: deploy calibration source and align the hexapod to feed the LGSW
Adjust the current value of the calibration source to get a ~10000 counts/subap on the blue pupil looking at the PnCCD viewer
Note the calibration diode number corresponding to blue pupil and its current value
Switch off the other 2 diode sources
Go up on the telescope, mark the fibers coupling to the diode module in the CalSource rack and then unplug all fibers
Plug, once at the time, all the 3 fibers on the active diode source
Take a snapshot and write down the flux value on the illuminated pupil
Measure LGSW entrance window in reflection
Switch on the LGSW internal source diodes
Adjust the current value of the calibration source to get a ~10000 counts/subap on the blue pupil looking at the PnCCD viewer
Write down the diode number and current value
Switch off the other 2 diode sources
Go up on the telescope, mark the fibers coupling to the diode module in the LGSW rack and then unplug all fibers
Plug, once at the time, all the 3 fibers on the active diode source
Take a snapshot and write down the flux value on the illuminated pupil
Evaluation of the differential LGSW EW transmissivity
The ratio between the pupil flux recorded in transmission and reflection should give a hint of the EW transmissivity. Obviously this is not an absolute transmissivity measurement, but only a differential one with respect to the blue EW value that has been taken as a reference.