I used to have my instruments checked every two or three years but it was a waste of time.
altimeters are calibrated to within 100ft of actual.
I could never understand why my altimeter on the ground never matched the QNH settings of others. they were calibrated but they never ever agreed.
so I came to the opinion that aviation instruments were crap.
as a surveyor I am well accustomed to calibrated precision instruments.
one day I was collecting my recalibrated instruments.
the guy (lacewing) said thank god you've turned up. you were the last customer and now I can retire. thank fcuk for that.
as I took the instruments out the door he shared with me this little gem...
"you homebuilt guys haven't got a hope you know. I always calibrate your instruments so that no matter how well you fly you always appear in the circuit at the wrong height."
why I asked.
"got to maintain the need for a certified environment you know".
well as the years have rolled by since I now have 5 altimeters.
I also have access to the kollsman instrument adjustment manual.
I adjusted all my altimeters sitting beside an IFR certified instrument (sitting on the ground in the copilots seat one day.)
only since I have adjusted them do I have 5 instruments that always agree within the 100ft tolerance.
Dick, even when you do get them calibrated, you can't trust the work done.
I swing my own compass. it isn't hard to do.
they are only accurate to 5 degrees. they aren't marked any finer than that unless you have a tiger moth P2 style compass.
you really only need to work on the compass if the rotation of the card becomes erratic due to the peening out of true of the tapered pivot post.
or they develop a leak.
havent had a problem with mine in a decade. it is tucked away out of the heat at the bottom of the panel which helps.
calibrations are yet another set of sensible ideas developed to idiocy.
W8