Method and apparatus for monitoring and/or correcting of a physical characteristic

A control signal modifying system comprising a source of input signals corresponding to sequentially occurring measurements, first and second storage means, comparing means operatively connected to said input signal source and to said first storage means for continuously comparing said input signals with signals stored in said first storage means to produce difference signals means operatively connected for adding a predetermined proportion of said difference signals to the output signals, of said first storage means to produce a corrected mean value signal, circuit means connected to said adding means and to said second storage means for applying said corrected mean value signal to said second storage means for storage, signal transfer means operatively connected to said first and second storage means for transferring said corrected mean value signals from said second storage means to said first storage means, and control means operatively connected to sequentially control said first and second storage means and said signal transfer means, whereby signals stored in said first storage means correspond substantially continuously to the mean value of said input signals, and wherein said first storage means comprises counter means, said second storage means comprises analog storage means, said means for adding comprising a source of pulses, said system further comprising means responsive to the amplitude of signals stored in said second storage means for controlling the number of pulses applied from said source of pulses to said counter means of said first storage means.