Is this oil pressure ok?

Quality electric gauges can be accurate, they should be checked against a knowen good mechanical gauge. Where is the sending unit for the electric gauge installed?
The sending unit is installed next to the distributor, I have had it for a few years as well and at one point accidently had wires backwards on it, but it still managed to work which is weird. Also it's a marshall gauge? Are those any good? Debating on buying a mechanical stewart warner or auto meter