Protection against shocks: since the pendulum is kept still by the torque motor, there is practically no moving part while measuring: there are mechanical stops that do allow only a very small arc of movement even when not electrically powered.
Accuracy and repeatability: the closed loop circuitry allows a big reduction of the only error that can be introduced into the measurement, that is the friction: a tiny movement allow a tiny error.
Calibration: every axis have this external resistance that can be used to have the unit to simulate a certain value of tilt described in the calibration certificate (provided there is no horizontal misaligment on the customer's fixing plane)
Auto checking: periodically it is possible to use the calibration resistance and if the output is not what expected, something is wrong.
High sensitivity: the longness of the sensing pendulum allows an high sensitivity even to small variations of tilt.
Broad bandwidth: the broad bandwidth allows to measure even sismic vibrations from 0 to 50Hz (series ES261 is able to give a signal even at 0Hz, where sismograph are not able to measure).