Dave Plowman wrote:

the gauge is still poor.
About 25% out at 30 psi.
Is it really impossible to make a gauge which actually works?

I have a halfords one, not exactly the same as they currently sell, but
very similar

https://i.ebayimg.com/images/g/a5EAAOSwSxtd39KW/s-l1600.jpg

The digital gauge agrees very well with my simple analogue dial gauge