This is an electronic digital caliper to computer (RS-232) interface. This will work with the inexpensive calipers, micrometers and height gauges that are typically made in China. The connector on the measuring instrument will have 4 pins, and the owner’s manual will typically describe the output as 24 bit 90 kHz synchronous. This does not work the name brand instruments - Fowler, Mitutoyo, Brown & Sharpe, etc.
The caliper sends a burst of data approximately three times each second. Each burst contains 48 bits of data as shown in timing.pdf. The first 24 bits are the position relative to the zero point set on the caliper. The second 24 bits are the position relative to an arbitrary zero that does not change. This is sort of an absolute position, but the zero point changes each time the caliper loses power. Each 24 bit value is in ones compliment form (1 sign bit, 23 data bits). This allows for a 0 and a -0. The unit of measure is 1/20480th of an inch. [image source: www.hobbytoolsupply.com]
Digital caliper to computer (RS-232) interface [Link]
