https://www.amazon.com/ACDelco-ARM6...;hvtargid=pla-4583932713325041&psc=1looks similar to the Harbor Freight digital unit but in a different outer case colored bright CCP red.
I used the now gone 20% off coupon and bought the Harbor Freight digital intending to return it if was way off.
I had 3 torque wrenches that the instrument shop at Oak Ridge National Labs instrument shop crew had tested for me during their once per year “Family Day.”
The HF digital unit tested +/- 1 ft-lb at 100
I was surprised, but testing 1 is not like testing 20 randomly purchased units.
Remember you can test one torque wrench against another using star shaped sockets.
If you have an accurate weigh scale,
You can also test torque wrenches
by clamping the square drive in a vise
and hanging known weights from a known length handle
when the handle is as near perfectly horizontal when under strain.
Use the cosine of angle correction if the handle angle is not horizontal.
If everything is not moving and still, there cannot be torsional friction at any joint. Friction requires movement.
Do not get too excited about exact torque because torquing a fastener is so inexact anyway. Bolt stretch is way better.
You can test pressure gauges with a high vertical pipe and distilled water.
You can test temperature with the freezing and boiling temperature of distilled water but correct boiling temp for your altitude.
The accuracy of those “gravity wave” detectors is unreal.
