Hi there,
I might be mistaken, but if memory doesn't fail once again, it's something to do with the slightly increased dial thickness for enamel dial. "H" beeing indicative for "haute" french for high.
But I'll try to get some bettre info on that.
Meanwhile, you might have a look (and listen :-) ) here....posted by Thomas some time ago. Hope the file's still present.
click on the picture to download the sound file of the 3939H - about 500kb
be sure to turn up the volume on your computer speakers.
You will need a media player compatible with mpg files.Best regards
Suitbert