"Calibration targets" refers to specific objects or materials that are used to ensure accuracy and precision in measuring or adjusting equipment. Full definition
Filmed at the site of military - use photo calibration targets in the California desert, the artist proposes becoming smaller than a pixel, the personal use of green screen technology, and more. (sfaq.us)
Additionally, the team behind Mars2020's SuperCam instrument will be adding a Martian meteorite to their own calibration target. (spaceref.com)
Previous NASA rovers have included calibration targets as well. (spaceref.com)