Scanning tunneling microscopy (STM) is well known for its high lateral resolution and nondestructive surface profiling capability but its potential as a profiler for dimensional measurement has rarely been exploited because of its unreliable vertical accuracy. In NANO III, a STM was presented that was capable of 250 mu m line scanning secured by a parallel spring mechanism in the X direction; it employed an interferometric monitoring STM tip, allowing feedback controlled motion in the Z direction. For this device, errors of step height and pitch measurements on a surface topography standard are estimated. The uncertainty of the 3 mu m pitch and 100 nm step height measurements using the STM is 1.05 and 0.41 nm, respectively. The uncertainties are induced by thermal expansion, the motion of the scanners, the nonlinearity of the interferometer, and geometrical error. In the 100 nm, step height measurement, the sum of the standard deviation of the measured data and the total error is still in the subnanometer range.