Invention of the clapperboard/synch slate

Hi there,

I am researching the invention of the clapperboard (for my master thesis) and I am wondering of there is someone out there who knows more than wikipedia or the imdb note about it?

https://en.wikipedia.org/wiki/Clapperboard
http://www.imdb.com/name/nm0502499/bio?ref_=nm_ov_bio_sm

It must have happened sometime when the "talkies" began and the film industry adopted to the production of sound movies.

I would appreciate any hint or help!

Thanks a lot!

Hanne