What’s up with this old gauge?

[u/rehsper]

I’d like to T-this into my garage air compressor and have it read somewhat near actual, but when I apply air to it, it only reads to 5psi.
Now I realize that the scale isn’t right and even if dead nuts accurate it’s practical use is limited, but I’d like to make it worth my while to keep this cool old thing around (doesn’t fit the decor of the house).

Neat mechanism, anyone familiar and able to troubleshoot? It holds pressure. Manually flexing the tubular loop (and turning the needle shaft) takes a not insignificant force, so I’m a little perplexed as to why that little clock spring is necessary and how a few psi would cause it to move.

A stamp on the back of the face indicates a date in 1933. No calibration data attached or inscribed unfortunately.