"The 'STOP' key is essentially an 'all notes off' command. It takes Sinfonia out of any mode where music is still playing and puts it into STOP mode. It is essential that you hit the 'STOP' key when you are finished tapping, but you are still in the middle of a song. Failure to do so can cause Sinfonia to crash. Instances like this can occur in many varieties: during rehearsal you may be tapping a sequence and the rehearsal is momentarily stopped. You are in the middle of a song, and because you are not tapping, no sound is being generated by OrchEXTRA. However, the computer thinks you are just 'between taps' unless you press the 'STOP' key. If you try to resume tapping, or give Sinfonia another command, it will try to calculate a tempo based on your last tap (maybe several minutes ago). THE SYSTEM WILL CRASH! Another scenario: The end of a song requires manual tapping because you are following the singers, etc. You tap through the last note (which may or may not technically be the end of the sequence), but you don't press the 'STOP' key. Again, the computer will think it is still in 'PLAY' mode and when you go to the next command it will CRASH! The last thing you need is a CRASH in the middle of a performance, but it will be your fault alone for not hitting the 'STOP' key! You can try and blame Sinfonia, but in your heart you will know it was all OPERATOR ERROR! "