EBC and analogue gauge innacuracy/ discrepancies

I've been running a manual boost controller (ball and spring) for the last couple of months with ananalogue gauge, I'm unsure of make but it looks like a copy of a VDO unit, I've been running 16psi on h-dev 1a chip

Anyway I've bought a greddy profec a controller but it's the older unit, as its second hand I've had it setup to test off the car with a power supply a bike pump and boost gauge and there are some inaccuracies
The greddy unit shows 1.2 bar which should be 17.5 psi but the analogue gauge shows nearer 19psi

Which would you believe EBC or analogue ?

Is there anyway to actually check them ?

Thanks