We rarely think of IWC watches with chronometer certificates and when we do we think of Switzerland but from the late 1800's, Stauffer, Son & Co., the English distributors of IWC submitted watches to the National Physical Laboratory in Teddington/London (Kew Observatory) for testing.
Part One:
Part Two:
Sadly the author, Friedrich Wagener, has passed away and his excellent website is no longer available but a pdf file of the above with images is available in the internet archive (link below). The link is very S.....L.....O.....W..... but the full article is worthwhile.
Cheers from the cellar