Uncompensated thermomechanical errors in laser tracking interferometers are examined by evaluating the difference between tracking interferometer compensations in a controlled laboratory environment versus being compensated in a factory environment. The hypothesis under test was that compensation in a factory environment does not adversely affect, and may actually improve, the uncertainty of laser tracker systems. This hypothesis was confirmed by measuring a standard (i.e., linear interferometer) using laboratory- compensated and certified instruments, and then compensating the instrument in the factory environment and re-measuring the standard. The results showed that in-shop compensation generates less variation in the measurement of the standard when compared to the laboratory-compensated and certified instruments. Certified weather stations are used to compensate for the uncontrolled atmospheric effects on the range measurement.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.