  We describe new results from the semiconductor-laser tracking frequency
gauge, an instrument that can perform sub-picometer distance measurements and
has applications in gravity research and in space-based astronomical
instruments proposed for the study of light from extrasolar planets. Compared
with previous results, we have improved incremental distance accuracy by a
factor of two, to 0.9 pm in 80 s averaging time, and absolute distance accuracy
by a factor of 20, to 0.17 $\mu$m in 1000 s. After an interruption of operation
of a tracking frequency gauge used to control a distance, it is now possible,
using a nonresonant measurement interferometer, to restore the distance to
picometer accuracy by combining absolute and incremental distance measurements.
