I am converting Beethoven's 5th Symphony to MIDI. However, I am stuck on the meaning of "a2" above some of the woodwind parts. As far as I can ascertain, a2 means "with the second flute (or other instrument), but I have no idea whether this applies to one note, one bar or is in force until the notes for both instreuments are shown together or "1." (meaning: first instrument) is encountered. Can anyone give me the true explanation please?