The renstemningsautomat , or automatic pure-tuning device, determines which particular pitch variants are required to produce just intervals and chords, with preference usually given to the pitch or pitches that previously sounded most recently. At any given moment there are twelve 'open' relays connecting 12 pipes (plus all of their octave equivalents) to the 12 keys on the manual, and 24 closed (inactive) relays. When a given note is actually played on the manual, that particular pitch is flagged as an active pitch. When a chord is played, whichever chord member was most recently flagged is designated as the reference point for tuning the chord. In other words, if possible, the flagged pitch remains fixed and the other chord members are adjusted (if necessary) in relation to that fixed pitch.

       Whenever a particular pitch frequency is given priority as a reference point, the automat 'locks-out' a designated set of incompatible or out-of-tune pitch frequencies (i.e., out-of-tune as determined by Groven's aesthetic priorities). Any of the open relays currently connected to an 'incompatible' pitch, are automatically switched to a compatible one--before the next notes actually sound. Hence, the automat is continuously anticipating which particular pitches might be needed so that those relays will be open and standing by. As such, the renstemningsautomat not only adjusts simultaneously-sounding harmonic intervals, but melodic intervals as well.

        Within an unlimited pitch universe, this type of procedure would, of course, lead to a continuous drifting of pitch. To ensure that a modulating piece of music can return to the exact same starting tonic, the performer selects ahead of time one of fourteen pitch-fields, each containing only 22 of the 36 pitches. Each pitch-field is capable of suitably rendering approximately twelve different keys (some major and some minor) in just intonation. This does not necessarily imply that any key outside of this set is unusable, but rather that it will contain some triads which are not just, and hence there would be some degree of key coloration. As an alternative, it is also possible to change pitch-fields in the middle of a performance with little difficulty.