Not sure I would be to confident in the accuracy of a Harbor freight guage

 

Accuracy is not as important as just being able to see a change in normal readings.

 

"You do not need a $200 gauge for the cab - and anyone that tells you that doesnt know what they are talking about. Ive had a $50 mechanical guage in my cab for 7 years now. Its never missed a beat and never leaked a drop of fuel."

Dr. Evil, Do you remember where you got it from?