A NIST computer model called "SuperFit" compensates for a common source of error in coordinate measuring machines and promises to increase greatly manufacturers' ability to check accurately the shape and dimensions of products. Touch trigger probes consist of a sensing element and ruby-tipped stylus. As shown in the graphic, the probe triggers each time it touches the part (white lines show touch points). When measuring a "perfect" sphere, a typical probe stylus bends and the tip may move slightly when contacting the sphere at certain angles, causing measurement errors. Red to yellow areas show where the probe overestimated the sphere's true size. Blue areas show where it underestimated it.