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Hello Joe,  Yes that is what I was talking about.  Which make is yours?  Hamilton made the most, but Waltham and (I believe) Elgin made very similar pieces.  Beebe said that he was concerned with making it as easy as possible for the lone sight taker to function effectiviely.  His original attempts were to use a note card sized piece of plywood attached to his forearm (with note cards attaahed with elastic) and a seconds setting wrist watch.  I assume he later moved to the Heur seconds setting rally watch because it's bigger and easier to read...and less easy to make mistakes.   I assume he never went to stop watches, because they require either two hands, or one hand also moving/adjusting  the index arm.  I wonder if the people who use (either mechanical or quartz) split seconds timers, don't have an assistant to work the watch.  As I've siad, Beebe wanted a lone watch keeper to be able to do the work him/herself.

On a related note, while surfing the net for any items to attach a GTC watch to the plywood, I came upon a site that sells wrist straps with adjustable holders for pocket watches.  I'm tempted by one myself. 

Cheers,John