Tire Pressure Gauge Accuracy

[obob]

Recently I bought a tire inflater that I returned but it came with a digital cool looking gauge and I notice it read 5 psi more than the gauge I was using.  I was using a 4 year old Victor I got from Autozone that I have kept inside the car.  I kind of assumed the new cool looking digital one was correct.

 

So I bought an arguably highly rated Accutire guage

https://www.ebay.com/itm/NEW-Accutire-MS-4400B-Pistol-Grip-Digital-Tire-Gauge/332190079729?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649

 

And I also bought an inexpensive pretty ebay guage from China 

https://www.ebay.com/itm/New-Auto-Motor-Car-Truck-Bike-Tyre-Tire-Air-Pressure-Gauge-Dial-Meter-Vehicle/371524205456?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649

 

 

The Accutire gauge allows for zeroing it out.  So I did that and there was a 1 psi change in readings which after that were consistent, though as I think about it more, I may have just lost 1 psi of air in the zeroing out process.

 

Comparison

 

Accutire 55 psi

Victor     56.2 psi

Ebay inexpensive  50 psi

 

They each make consistent readings so it seems I can use each of them with an adjustment.

 

I am going to assume the Accutire is the most precise and keep that inside rather than exposing it to heat and cold.

 

Ideally it would be good to know somebody that has a calibrated gauge to test the gauge I use for my baseline.

 

 

I don't think I can assume that the pressure precision would be the same at a different pressure, like a more standard 38 psi.

 

 

By the way, the inexpensive gauge comes apart and it is like a short pencil gauge and the part that pops out pushes against the dial readout so perhaps I could shim it up to get a better reading or grind off some plastic do it goes in further.

 

 

PS I would like the change the title to use the word precision rather than accuracy.  All three gauges are accurately consistent.  Not sure how to change that.

Edited February 10, 2018 by obob

[SnowStorm]

Your title is correct.  Accuracy refers to how nearly "correct" the reading is while precision refers to how fine the readings are (the resolution).  The Accutire says it has a resolution of 0.5 psi (readout increments) and also claims an accuracy of 0.5 psi.  That's a bit of a stretch.  I would say they are just using terms interchangeably and who knows what the real accuracy is.  Plus, if it doesn't have traceable calibration you can't be sure of anything anyway.  I would also like to have a gauge with known accuracy but expect it will cost more than $12.  You can go all out and get this one with 0.05 psi accuracy for $900!.  Or, more sensibly, this one for $20 that claims to be "tested, certified accurate, & calibrated to ANSI B40.1 International Accuracy Standards (±2-3%)".  You will have to take their word for it because I'm sure its not traceable.  Note that this accuracy will only get you +/- 1.2 to 1.8 psi but it looks like a nice gauge.  It also locks the reading until you release it - a nice feature.  Hmmm, I might have to get one of these (or something similar).  BTW, "digital" brings with it NO indication of better accuracy.  All readings start out in the "analog" world and get converted to a digital value for readout.  Again, the resolution (i.e. precision) of the digital readout is no indication of accuracy.