Had a busy day, and not done a daily watch photo, so………let’s celebrate Citizen’s automatic mechanical chronographs 🙂 Introduced in 1972 the two variants of the 81 calibre are very well designed, compact high-beat movements, running at 28,800 beats per hour – 8 beats per second – all with 23 jewels. They have a fine adjuster on the balance for highly accurate tuning – if you have looked at Brian Leiser’s restorations on this blog, you’ll see in his comments how well these things can run. The 8100 has one sub-register, counting elapsed minutes, whilst the sweep hand counts the seconds. The 8110 adds a second sub-register so hours can be counted too. They can all be hand-wound, and of course have start and stop/reset chronograph buttons. And they all have ‘fly-back’ capability, whereby the chronograph can be reset instantly without having to stop it first. One of the nice features, unlike a lot of other chronographs, is that it is best to leave the chronograph running, since there is less load on the mechanism. So the smooth sweep of the second hand is always there 🙂 It is advised to run the movement with the chronograph stopped from time to time – this helps to avoid it seizing in the running position. The 8110 had a much longer production run, to the early 1980s, whilst the 8100 was perhaps only two or three years. The so called ‘bullheads’ are the most well known, but there are a good variety of other designs, some of which reflect the more colourful design trends of the 1970s. By the way, the correct model name is ‘Challenge Timer’. ‘All original’ ones are increasingly hard to find unfortunately, so care has to be taken! Always do your research before buying – my blog page is (I hope) a good place to start:
https://sweep-hand.org/citizens-vintage-chronographs/

Not a complete collection but here are mine, several of which have been serviced by Brian (aka 31 Jewels):

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