FC2Video

Early calculating devices and computers used mechanical digital to
analogue converters. This video describes one based on an arrangement
of metal bars called a "whiffletree" - also sometimes called a
"whippletree." It shows, briefly, the whiffletree used in IBM's
revolutionary selectric typewriter and then illustrates the principles
of a whiffletree converter by showing the simplest one - one that
encodes digital impulses into two bits of information. (This videos is
an appendix to Bill Hammack's video about the operation of the
Selectric Typewriter.)