Richard J Kinch wrote:

Duane Bozarth writes:

Gages are pretty unreliable, especially when under pressure all the
time.

???? A device designed specifically for the purpose is unreliable???

Absolutely. This is the nature of the Bourdon tube mechanism.

Many other ways of building them...

Ones one the system here last for several years at least and then it's
rarely the gauge itself that fails, it's accumulated rust/sediment.

Units work in power plants for years as well...but, of course, they're
industrial units.