Stewart Warner vacuum gauge was not steady at idle

Or just pinch the line. But I would leave it, because it's telling you the truth.
On an engine,closer to stock spec, it won't be doing that anyway.
But honestly, I don't see any value of having a permanently installed Vacuum gauge.
Nor for that matter, an engine oil-temp gauge.
But then the only decent gauge I run is the tach, and I hardly ever look at that either..lol.
I'm a streeter tho, I'm real busy keeping it between the curbs.

lol