I’m looking to get one to do bike tyres, car tyres and water expansion tank, so needs to be accurate enough from about 15psi/1Bar (bike tyres) to about 60psi/4bar (van tyres)

There’s loads on eBay for under a tenner, some branded, some seemingly identical but unbranded, do I assume they’re all coming out of the same Chinese factory and they’ll do the job?

https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2380057.m570.l1313&_nkw=digital+tyre+pressure+gauge&_sacat=0

Unfortunately not.
Tolerance of about 1 bar on the one a friend was using on his bike tyres. Problematic on his road bike, nightmarish on his MTB. (tested against a fluid filled and (fairly) recently calibrated gauge).
The replacement was better, but still up to ~0.5 bar out. Which i could live with on a road bike or in the car, but not an MTB.

That was same model, same supplier (eBay special).
He’s got a third now (topeak i think) which is ok.

Ah, fair enough. So, what’s good for MTB tyres then?

He’s got a topeak one, was about €30-35 i think.
I have a fluid filled gauge attached to a hose and pump head (and a separate fluid filled gauge on my track pump too). So except for the losses through the valve (minimal) i get a pretty good/accurate/repeatable measurement.

I got one of these:

Lifeline Digital Pressure Gauge

after looking about & seeing mostly positive reviews for it.
No complaints here, although I have no way to verify how accurate it is.

Actually, the only complaint is that the auto-off function kicks in a bit soon. Not really a big deal though.

I’ve had the yellow and grey topeak one for years. Seems to work great.

I finally bought https://www.merlincycles.com/schwalbe-airmax-pro-digital-pressure-gauge-148933.html the other week, but yet to compare reading to the PX track pump gauge.

I have a couple of topeaks (d2?). Yeah work fine and both read the same. Whether that’s the same as something that has been calibrated, I suspect not, but it’s good enough for bikes/cars etc.

Cheers all. You know what, I never thought to look if there were actual bike ones from actual bike shops… *slaps head*

I bought one before and found it was very inaccurate

Also have the topeak one which reads the same as my track pump so now seems like a pointless purchase.

So how does one find or get to use a gauge that is calibrated and accurate ..in order to compare readings with your various home gauges? Where could I go to get an accurate reading ?

IIRC the place I bought my fluid filled gauges from offered a calibration service as well. Or you could just rely on the factory calibration. Which was free.

Topeak one is good ime.

Repeatability is way more important than accuracy though. Do you care if you have 16psi or 20psi? Nah, all you care about is that you have the amount of air that you want. Accuracy gives a little bit of usefulness across multiple tools, but generally if you have a digi gauge that’s your point of truth so it doesn’t matter if your floor pump reads 5 psi different either, you just get used to that. And pretty much nobody controls all of their air pressure doohickeys- sooner or later you use a mate’s pump or a co2 can or something.

Repeatability is way more important than accuracy though. Do you care if you have 16psi or 20psi? Nah, all you care about is that you have the amount of air that you want.

This.