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4. What About Unresolved Systematic Errors?

Go back to our mistake-free measurement set: MPV = 45.662 ±0.013; EMPV = ±0.006.

What if these are distances measured with a steel tape and we find out later that the tape started at 1.00' instead of 0.00'? What happens to our analysis?

Well, the MPV changes because each measurement is 1.00' too large (e.g., 45.66 should be 44.66). You can recompute the MPV or just subtract 1.00' from it: MPV = 44.662

How about the standard deviation and MPV error?

They don’t change because the residuals don’t change: since each measurement and the MPV lose 1.00', the residuals stay the same.

But remember that with the systematic error present, the accuracy indivcator (EPMV) is still pretty low which implies good accuracy. Go back and review the targets, particularly Figure C-1(b). An unresolved systematic error will affect accuracy.

So accounting for the systematic error: MPV = 44.662 ±0.013; EMPV=±0.006. That’s the nice thing about systematic errors: you can often eliminate them by computation.

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