HP 8568A Cal output adjustment

[Simon Spiers]

Hi  again another 8568a related question.
When i used to cal the -10dBm level using rcl 8 from the nvr i could adjust the level with the preset on the front panel .
My latest attempt has failed to show any shift in the level which is now off the top of the scree .
What i need to know is this.
Does the trimmer adjust the input gain of the generator or Cal level?
It looks like its tied to the a16 board?