1. The value read out at the left edge of the threaded probe holder is the distance between the threaded probe and the probe at the end of the scale.
2. Put the magnetic probe into one end of the size to be measured, loosen the fastening bolt and move the middle casing inside the main ruler, the value shown at the right end of the large casing of the main ruler is the distance between the magnetic probe and the probe at the end of the ruler.
3. Put the magnetic probe into one end of the size to be measured, loosen the fastening bolt and move the middle casing inside the main ruler, when the middle casing extends to the end, the positioning pin will pop out, then pull out the small casing of the main ruler to measure the ruler. The value shown at the right end of the middle casing of the main ruler is the distance between the magnetic probe and the probe at the end of the scale.