The Silence for Unison Tuning switch causes the normal sweeping sound to be muted when the software detects that you have begun to tune the unisons for that note after having tuned one string using the sweeping sound. This feature may be useful when tuning without a temperament strip and tuning unisons as you go.  The reason for using this feature is that after you tune one string using Montal Tuner, usually you will proceed to tune the other strings of the unison to that first string aurally.  But if Montal Tuner continues to make its sweeping sound, that can interfere with your ability to hear aural beats when tuning unisons.  That's where this silencing feature comes in.  When Silent for Unison Tuning is enabled, Montal Tuner will detect the pause that occurs after tuning one string and switch to a silent mode which is indicated by three short beeps.  Montal Tuner will remain muted until a note change or a visit to the Settings page.  Either of these actions will reset the silent mode and return to normal sweep sound generation, which is useful if the silent pause is detected before you are actually ready to tune unisons.