Machinist and cal-lab nickname for gauge blocks, taken from the Swedish inventor of the stacked block system. They are lapped to length and flatness within a fraction of a micrometre and can be wrung together into almost any length from a set of 81 or more blocks. Labs calibrate them by mechanical comparison against master blocks or by interferometry, and they carry dimensional traceability down to the shop floor.
Wring up a 37.5 mm stack from the Jo blocks and check the micrometer at three points.
Also heard as
- Jo-blocks
- gauge blocks
- gage blocks
- Johansson blocks
Related terms
Artifact
A physical object that embodies a known value of a quantity, such as a mass, gauge block or standard resistor.
Reference temperature
The standard temperature at which a quantity is specified, 20 degrees C for dimensional measurements.
Soak
Letting an instrument, artifact or part sit in the lab environment until it reaches thermal equilibrium.
Working standard
A standard used routinely to calibrate instruments, itself checked against the lab's reference standard.