How do You read a CNG gauge?

[dockhow]

I believe I have a 20 hour 84 cubic ft tank. Does anyone have a chart how to read the gauge to figure out how much time you have left based on the pressure?

C34 1987

[Stu Jackson]

My experience is that it is linear, engineering-eese for straight line.  We've never had reason to try to "calibrate" it, because we have a backup tank on board at all times.  The backup tank is located, well padded, in the forward salon port settee base, forward of the holding tank.  A hole was drilled to allow the knob to slide through into the lowest section of the port drawers and lowest swinging door in the V berth.  Just the other day a friend ran out of CNG, thought he was OK until he tapped on his gage.  He's got my spare now.