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+# Compensating Development Timer
+
+Developing traditional film and silver paper is very temperature
+dependent.  The warmer the developer solution, the less time the film
+or paper needed to be developed and vice-versa..  Historically, people
+read the temperature and then manually corrected their development
+time accordingly, using a correction table provided by the
+manufacturer.
+
+It turns out that these corrections for temperature are quite similar
+across different manufacturers, although the corrections *are*
+different for film and paper.
+
+Many years ago, a company called "Zone VI" realized this and created
+an analog timer that corrected for this effect.  You placed a
+temperature probe into the developer and it corrected - via analog
+adjustments - what a "virtual second" actually had to be.  The
+photographer just looked up the normal development time for 68F
+developer and the timer ran faster or slower based on the actual
+temperature.  Better still, if the temperature of developer varied
+*during* development, it corrected for that in realtime.  The Zone VI
+Compensating Timer had settings for film, paper, and realtime.
+
+The timer was a work of genius engineering and a really nice
+addition to the serious photographer's wet dakroom.  I've depended
+on one of these for years to make my darkroom work repeatable
+with minimal thinking or measuring.  Mine is getting kind of old
+now and I began to wonder what I would do if it broke.  The timer
+did come with a "Lifetime Warranty",  Sadly Zone VI and
+its founder, Fred Picker, are both now long gone making warranty
+claims ... difficult.
+
+While I could design an analog replacement or just figure out the
+circuit of the Zone VI, it occurred to me that it would be easier to
+just design a "work alike".  Thanks to the explosion of interest
+in robotics and the Internet Of Things, there is an embarassment
+of riches of computers, sensors, switches, temperature probes,
+and so forth.  Not only can we build something like this ourselves,
+doing so has several advantages over the old Zone VI timer:
+
+    * It's digital, not analog, so we don't have mess with
+      a bunch of precision parts and corrective feedback circuits.
+
+    * It's software controlled so you can customize how this
+      timer works to suit you.  Don't like my compensation factors?
+      Want to adapt this for a different application?  Both are
+      easily done with software changes.
+
+    * It's cheap.  You can build one of these for well under $50.
+      (The original Zone VI timer was around $200 if memory serves,
+      and that was when money was still worth something. :)