You got a way to test that that doesn’t require a gauge?
I suggest you start by reading I make terrible distillate....why?
And post pictures of YOUR setup.
Don’t have a gauge (Digital!!) ?
Are you the diy type?
See: Budget Digital Vacuum Sensor, read a 60$ pirani gauge through your PC
Why are you doing this under vacuum? (You need to, why?!?).
If you don’t know how hard you’re sucking, you don’t know the bp.
If you don’t suck, it’s 425-430C (probably)
Musings of a Cryogenicist: Day 5 – Vacuum Gauges (everything you wanted to know and more!) | HYdrogen Properties for Energy Research (HYPER) Laboratory | Washington State University might help understanding why you can’t use an analog (Borden) gauge here.