I'm a novice so the first thing that came to my mind is why do I need this expensive little metering gauge?
The Carter gauge is tapered, at a specific angle, to a point and sits inside the main jet.
If you measure from the shoulder of the gauge to the tip of the gauge you will not read 2.795 but something greater.
The distance 2.795 is from the shoulder to a point where the taper contacts the jet inside.
Needless to say it's not accurate to measure this distance with calipers as compared to using the gauge.
If you had a properly set carburetor you could measure from the gauge shoulder to the top of the jet and use this distance as a reference.
However, the jet in another carburetor may not be the same height or the gasket below compressed more.
In a nutshell, the gauge makes measurement easier and the accuracy better.
Also notice step 40 and 41 of the W1 service PDF.
I may be wrong but there needs to be one more step.
Back off the throttle adjustment screw (not idle adjustment screw) so that the throttle valve is completely seated (closed).
The pin of the pump should lightly touch the gauge shoulder. You want to triple check before making any adjustment.
Your carburetor is 80+ years old.
If there is wear in your throttle arm, throttle connector rod, pump arm shaft or it's connecting hole then your precision setting may be for naught.
