In microelectronic applications, electron beam measurements are frequently plagued by electromagnetic interference and vibration in the fabrication environment. In the past, efforts to control environmental effects have focused on attempts to decouple the measurement apparatus from the source of interference. Rerouting power cables, balancing phase loads, shielding with mu-metal and copper screen, isolating on concrete pads, and mounting on vibrationally damped columns have all been tried with some degree of success. The com-mon problem with these active solutions is that retrofitting an existing facility can be prohibitively expensive. We have found, however, that where environmental effects are relatively well known, they can be removed from the data a posteriori. In particular, 60-Hz electromagnetic interference, appearing as sawtooth patterns in non-synchronous SEM images, is probably the most common deleterious effect experienced in fabrication areas. Techniques are demonstrated by which tuned integrating and differentiating filters can automatically reduce the measurement error by as much as 80 percent.