Improved rig for dynamically calibrating skinfold calipers: comparison between Harpenden and Slim Guide instruments

This article describes an improved rig for the dynamic calibration of skinfold calipers. The new unit is 5% lighter and almost 60% smaller than its predecessor (Carlyon et al., 1996, 1998) with a 9.5 mm solid aluminium base and a quick release caliper mount providing stability to both the rig and caliper. Automation of the gap controller with an electric motor standardizes the jaw opening and closing velocity, thereby enabling hands-free operation. Frictional losses in the moving components of the rig have been reduced by replacing the main bush of the swing arm with a bearing, reducing the mass of the swing arm, adding a support wheel to the end of the swing arm, and replacing fishing swivels with a universal joint to allow for changes in the opening screw angle as the caliper's arm moves through its arc. This rig can also be adapted to different types of calipers by changing the position of the load cell, microswitches, and the caliper mount. A universal mounting bracket that can be secured to almost any table supports the rig in a vertical plane when calibrating the load cell. To demonstrate the versatility of the calibration rig, preliminary data are presented for the upscale and downscale jaw pressures of seven Harpenden and seven Slim Guide calipers.