Pressure gauge calibration

I see a crescent shaped slot at the bottom of the linkage coming from the semi circular air chamber maybe adjusting the position on this linkage may help
Plus the slot on that screw looks nibbled as if someone has already had a go at it with the wrong sized screwdriver or maybe its a trick of the light !!
 
I see a crescent shaped slot at the bottom of the linkage coming from the semi circular air chamber maybe adjusting the position on this linkage may help
Plus the slot on that screw looks nibbled as if someone has already had a go at it with the wrong sized screwdriver or maybe its a trick of the light !!
Yes that’s the screw I needed! They all agree now at least!
 
I suspect with the grossly inaccurate ones they've been over pressured and skipped teeth on the gear rack. Sometimes the needle is just a push fit on the shaft and can be persuaded off and replaced at the correct reading. Hopefully the sensitivity and zero will not have moved.
 
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