1. A method for monitoring an exposure of a system to a physical variable, the method comprising: A) periodically sensing the physical variable to produce a sequential digital data stream having a plurality of digital samples wherein the physical variable is acceleration; B) collecting a known number of digital samples in sequence from the sequential digital data stream to form a first time domain data group; C) applying a windowing function to the first time domain data group, the windowing function minimizing a difference between a value of a first digital sample of the first time domain data group and a value of a last digital sample of the first time domain data group; D) converting the digital samples in the first time domain data group to respective frequency domain representations in a frequency domain after applying the windowing function to the first time domain data group; and E) calculating the exposure of the system to the physical variable in the frequency domain using the frequency domain representations; wherein step A) is performed using an accelerometer sensing the acceleration in at least one direction.