This thread might be of some use to you. You do need to figure out what unit of measurement the vac gauge is in. Could be mmHg/torr or microns of mercury. This is my uneducated opinion, but I would guess the boiling point of CBD to be 450C plus or minus 15C at 760mmHg. Knowing that might help you make adjustments for distillation temp at whatever vacuum depth you are pulling - after stripping terps.
I’ve never distilled before so take with a grain of salt.