Hello Ned,

I don't have access to my small collection of books to provide you with a definitive source.
However, there are some useful internet sources:

http://etheses.dur.ac.uk/699/1/4_-_The_Development_of_the_British_army_during_the_wars_with_France.pdf see p. 247
http://royalscots.tripod.com/sitebuildercontent/sitebuilderfiles/whistlecalls.pdf
http://revwar75.com/library/pace/37-light-OB.pdf
https://www.army.mod.uk/umbraco/Surface/Download/Get/4234

Hope this helps
Best wishes
A