Steve, Craig,

As has been stated the NBC was three notes.  The device will produce four 
notes.  Since it appears that the notes produced would be in human audio 
range.  I am going to guess a tuning device for a stringed instrument.

Tuning instruments that can produce sustained tones, beats can readily be 
recognized. Tuning two tones to a unison will present a peculiar effect: when 
the two tones are close in pitch but not yet identical, the difference in 
frequency generates the beating. The volume varies like in a tremolo as the 
sounds alternately interfere constructively and destructively. When the two 
tones gradually approach unison, the beating slows down and disappears, 
giving way to full-bodied unison resonance.

Beat frequency tuning was the old human ear method but it requires a 
standard device of correct frequecy.

Drew Meyer

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/ContentPage.aspx?Pageid=E-mail-Forums for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------