[from Isaac Upsal's instructions to star-ops, dd.May 17, 2023]

If stable collisions are available and the BBC (ZDC) is ready to use as a trigger then we can take the VPD gain scan. The procedure is as follows:
Make sure that you are using a **non-VPD-based** Trigger for all data taking.

First :
On the sc3 machine there needs to be a "small GUI" for the VPD with 4 buttons - upVPD HV A, upVPD HV B, upVPD HV C, and Default. If it is not open or you are unsure open a terminal and execute "upvpd_settings". I just opened this ~an hour ago.
"large GUI" shows all the channel values, and where one powers them on/off.
"small GUI" selects between different gain sets A, B, C, & default.

start with the VPD HV **OFF**

1) On the small GUI choose the HV Gain setting *A*
2) On the large GUI power on the VPD HV
3) Make sure that the upper-left corner (channel 13-0) of the large GUI reports a voltage of ( 1101, 1251, 1401 ) for gain setting A, B, and C respectively.
4) Wait about a minute or two for the VPD PMT channel voltages to settle
5) Start run: TRG+DAQ+TOF (it is OK to include other detectors in if you want, but those are required), 200k events. Use string "VPD HV A" (or B, C as needed) in the shiftlog entry
6) Use the "large GUI" to power off the VPD HV
7) Wait for all channels to read a voltage of 0

Repeat these steps for each of the gain settings (A, B, C) - making the appropriate entry in the shiftlog to identify which gain setting is used (upVPD HV A, upVPD HV B, upVPD HV C ).

Once this is complete, use the "small GUI" to select "default" then power the VPD HV back on. Now you can close the "small GUI".

More information on the software and analysis workflow can be found at this GitHub repository: https://github.com/RiceU-HeavyIons/BTOF-online/tree/master/gainfit