ultred ragnusen wrote:

1. Unmeasured five full-torque applications (e.g., 150 foot pounds)
2. Measured, five 20% torque applications (e.g., 30 foot pounds)
3. Measured, five 60% applications (e.g., 90 foot pounds)

Average it all out and you get your percentage error.

The nice thing about standards is that their are so many of them.

Most of the world appears to use the ISO 6789 standard.
http://www.nla.org.za/conferences/pr...esentation.pdf

This paper lists ISO6789, JJG 707, ANSI/ASME B107/14 & GGG 686D standards.
http://www.norbar.com/portals/0/ntts...ov08%20nab.pdf

While the paper above says all the standards are similar, it mentions that
ISO 6789 has the largest use. ANSI/ASME B107/14 is popular in the USA.
GGG686 is an American military standard which is being overtaken by
B107/14. And JJG 707 standard is used in China.

A key step is that the calibration device has to be within plus or minus 1
percent, which is really the difficulty for home calibrations, I think.

It's interesting to note that the calibration has to be done such that the
weight of the wrench is negated, which means you can't have the wrench set
horizontally and then push down on it, as gravity affects your
measurements.

Also it's interesting you always calibrate "up", in that you test the
smaller torques before the larger torques.

I've never calibrated my torque wrenches, where I have a few 1/2-inch drive
ones (beam and click), 3/8-inch drive (click) and 1/4-inch drive (click)
where all the click types are from Harbor Freight, so I'm unsure of
accuracy.

The problem is to find a calibration standard that is easier to use than a
bucket of water or dumbbells.