Abstract: Described is a writing instrument-caliper system composed of a fully functional writing instrument and a separate caliper device. The writing instrument and caliper device are of such construction that the caliper device can be inserted snugly into the open-ended hollow barrel of the writing instrument for safe storage. With the caliper device in its storage location, the writing instrument-caliper system is of similar outer physical dimensions to the writing instrument alone, and can be carried safely in a shirt pocket without risk of injury to the user or it can be employed as a fully functional writing instrument. With the caliper device removed from its storage location, the writing instrument and caliper device can be employed in parallel, allowing the user to make written notations while simultaneously making measurements with the caliper device. This writing instrument-caliper system overcomes many of the problems encountered by prior art devices.