That's where the TiCal Pro comes in, as it's a three-way caliper measuring tool that also lets you do some wrenching, bottle-opening, nail-pulling, and more. Currently the subject of a Kickstarter ...

Results Measuring total sitting time based on a workday, non-workday and on average had fair to excellent test–retest reliability (ICC=0.46–0.90) and had sufficient criterion validity against ...