This operation analyzes the MIDI song and suggests a song key that you can assign to the song.
It chooses the song key (number of # or b, major or minor) that will produce minimum number of #, b exceptions on a score sheet. Change the selected key if you want to set an other key.
Answering yes will write the song key information (META event) into the MIDI file.
Hint: A song could be printed on score sheet with any key, with a bad key choice the number of necessary exception symbols (#, b) within the measures might be high and the scores might be difficult to read.