Oil pressure gauge needle not on zero at rest

[70StepsideC10]

I recently picked up a bunch of used gauges, one of which is an 80lb oil pressure gauge. The gauge is not installed in the truck yet. The needle rests at about 15lbs rather than zero. I tested the gauge with my compressor, and it works fairly accurately, but off by 15lbs (35lbs when actually 20, 65lbs when actually 50 etc). I thought maybe the needle had just got moved on the shaft, but I tried holding the shaft and rotating the needle but it would not budge. Does anyone know how I can get the needle back to zero? Is there something on the gauge mechanism that can bend causing the needle to be off? The alternative would be to pull the needle off and just reposition it at zero, how would I go about removing the needle without damaging anything (it seems to be on there pretty tight).