Calibration convention question

[KenC]

Any engineers here?

If I determine that a meter is reading 9 units low, how do I mark the meter so others will know (and me when I forget)? "Add 9" or "subtract 9"?

(Happens to be for an anemometer)

Ken C

 

[denton]

indicated minus actual

A gauge that reads 5 when applied to a standard that is known to be 6 is 5-6=-1.

 

[Infidel]

I would mark it "reads 9mph low".

 

[Mizar]

Don't know, you tell me - if we subtract 9 units from the already subtracted 9 units we get like... 18 units low. About, maybe sort of... Rough estimate that is - need a formula...

 

[jeepnik]

You don't mark it. You either recalibrate it or replace it.

 

[WelshShooter]

A device is usually calibrated over its entire measurement range. Is your anemometer always - 9 units across its entire measurable range? What if your measured value is equal to 9mph or less?

If your device is that much different, then should you really trust it? In the engineering world, the item is adjusted until it is within an acceptable tolerance of error across the entire range. You would not usually slap a sticker on said device saying "subtract 9 from measured value" as that's considered bad practice.