TAR stands for test accuracy ratio: the tolerance of the unit under test divided by the accuracy specification of the reference standard, ignoring every other source of uncertainty. It is a simpler screen than TUR, used in procurement and procedure writing to pick a standard with 4:1 or 10:1 headroom. Because it leaves out environment, resolution and method effects, a TAR almost always looks better than the real TUR.
Procedure calls for a 4 to 1 TAR, the bench calibrator's spec gives us 6 to 1 at this point, so it qualifies.
Also heard as
- test accuracy ratio
- accuracy ratio
Related terms
TUR
Test uncertainty ratio, the tolerance being checked divided by the expanded uncertainty of the measurement process.
Four to one
The rule of thumb that measurement uncertainty should be no more than a quarter of the tolerance being checked.
Spec
Shop clipping for a manufacturer's accuracy specification, the published limits an instrument should stay within.
Tolerance
The allowed deviation from nominal that an item or instrument may show and still be accepted.