[en] A window and peak height converter circuit has been designed and built that extracts a single mass peak (or group of peaks) from a set of mass spectra repetitive in time and produces a time profile of that mass. The response time of the circuit is such that one has the capability of real-time operation and of operation on mass spectral data that has been prerecorded on analog tape. The use of analog recording of data allows a great deal of flexibility in recording and playback speeds, and more importantly produces a permanent record of all information contained in the mass spectral data