The early Concert Pitch at A=435 is also for 'unheated' spaces, and at
55 degrees F. The ANSI standard Concert Pitch is A=440 for more modern
heating indoors and 70 degrees F., give-or-take normal temperature
shifts.

The percussion instrument maker, J.C. Deagan, wrote a paper arguing
that in use there is no real difference, and his position was accepted
by the American Federation of Musicians, the political positions of
orchestras not withstanding.

Grant Chapman
West Point, New York