I would go to a local distributor and purchase a liquid filled gauge. The liquid / glycerin in the doesn't make it more accurate but they tend to be a better / more accurate gauge. Then try it again, especially since you had two very different readings.
Just another thought, what time was it when you took the reading? Was it about the same time in the day. Pressures can fluctuate depending on the demand in your neighborhood.
Josh
Irrigation /Landscape Lighting / Pump and Well Specialist