Digital tyre pressure gauge

In a fit of spending, I bought a digital tyre pressure gauge. Now I have accuracy, I have dilemma.

This gauge reads 2.35bar, old faithful reads 2.6, tyre inflator reads 2.5bar.

It's a small error - say 10% between them all.
Out of a desire to not break something and leave it alone, I opened up the gauge. It's got markings that suggest you could display more than just bar/psi. It's a Shineway pcb and uses a cr2032 battery. No ID on the pressure sensor itself.
It has a tempting box marked R9. Putting a 1k resistor on there reduced the pressure reading from 2.3b to 1.3b. Whether this was a fixed offset of a linear change throughout the range (ie slope) will have to wait until a fit of enthusiasm to play. Or until I stand on it and it breaks.
For now I'm going to assume it reads under by about 0.5b (or round up the result)

The car was serviced about a month ago. The rear tyre should be 2.1 and it reads 2.1 on the digital and 2.4 on the silver old faithful. Front should be 2.3 and read 2.25, old faithful was 2.7. The original battery, a 2032 was not enough at 2.8V to make it work. A 2025 fits ok.