App note from Bourns about the robustness of trimmers used on surveillance system, typically sealed to protect agaisnt harsh environment. Link here (PDF)
Trimmer technology is designed for use in applications where the unit must be calibrated before it is shipped to a retailer, and eventually the end user. Typically, these pre-calibrated electronics use a trimmer for required adjustments to account for component variations over time. Medical and industrial designs frequently take advantage of the system calibration convenience of a trimmer. In surveillance systems, the trimmer is adjusted to obtain the best resolution of the sensors at an
installation point.