The Moonwatch from The Emotion Lab will allow you to answer that question using the only chronology that really matters to werewolves: the current phase of the moon (it also tells the time too, but who needs a watch for that?).
Gizmodo’s writeup is appropriate: “This watch? Oh, it just warns me when I’ll turn into a berserk beast capable of ripping off your head, chomping your entrails, surfing on vans, hooking up with Willow, hooking up with Bella, you know, normal werewolf stuff.”
Edit: Sadly, the Moonwatch is not (yet) for sale: The Emotion Lab is an industrial design studio, not a retailer or a manufactory. If you want a Moonwatch of your own, maybe offer them a whole pile of money to turn the concept into a workable, sell-able item just hang on: according to this tweet, The Emotion Lab is working on getting the watch into production ASAP.