Watkins Darkroom Clock

​An Eccentric Darkroom Clock from 1911

A few months ago I bought from a friend a rather charming darkroom stopclock made by the Watkins Meter Company of Hereford. Watkins, of course, were well-known as part of the movement promoting a more scientific approach to exposure and development of negative materials. Their best-known product is probably the Bee Meter, of which most photographic collectors have probably got an example or three. The Bee Meter was made for many years, and this darkroom clock was, I am sure, part of their mission to make darkroom work more systematic.
Before this clock there was the Eikronometer, which in appearance was a rather more cumbersome clock, deep in the body, with an exposure calculator in the form of a couple of rotating brass rings at the back. I have not seen one of these in the flesh, but it does look quite awkward to use. The darkroom clock of 1911 could be used in conjunction with their Factorial Calculator (a disk-shaped calculator). It seems that the old Eikronometer was split into two - a calculator and a darkroom clock.
At first glance the clock looks very much like an alarm clock of the period. It has two splayed brass feet and a ring at the top to lift it by. It is marked ”Made in Baden”, and the actual clock is a Black Forest job, made by Philipp Haas & Sohne of St Georgen, Baden-Wurttemberg. Look a little closer however, and you see that instead of being calibrated from 1 to 12, the dial runs from 0-9 with 10 subdivisions between each major division.
It wasn’t running well at first, so I decided that a good clean of the movement would be a good step towards reliability. I took it all apart, cleaned everything and reassembled it – all quite straightforward if you have mended one or two simple clocks before. All back together, and it runs very nicely. But what is it saying?
My first thought was that it had a serious problem. It has a minute hand and a second hand, but the second hand took about a minute and a half to do the circuit! I started to think about what I would have to do to the balance spring in order to get it going at a more sensible speed. I am glad to say, however, that before doing anything drastic I called for help from another friend who was able to consult the Watkins Handbook. There it was explained that the intended operation is that the minute hand does the circuit in 10 minutes (so each major division is one minute), but for the second hand the major divisions show tens of seconds so that a full circuit of the dial is 100 seconds rather than 60. Which, given a few seconds of adjustable error, is exactly what it is doing.
So in the illustration below, the minute hand has travelled 7.6 minutes, which is 456 seconds. The second hand has of course gone around several times but is now pointing to 61, so the more precise measure of the time passed since the clock was started is seven minutes and 36 seconds. Putting it another way, at the exact full minutes the second hand will be pointing successively at 6, 2, 8, 4, 0, 6, … and so on.
And why?, you may ask. It seems to be intimately linked to the "Watkins Factorial Method" for plate developing. The idea is that you watch your plate in the developer, and using the second hand, time the emergence of the first visible details. Then using a factor (fixed for that developer) calculate the total developing time, which may be, for example, 5-10 times the time you noted with the second hand. Then you use the minute hand to give the calculated development time to the plate. So 30 seconds emergence and a x10 factor gives a 5-minute development time, which you read with the minute hand, ignoring the seconds indication.