Although it is not mentioned in the manual, it is possible to set up a clock in the HP-28S using a set of programs.
A while ago I got two 28S and loaded the programs. I do not use a watch, and I always find out what time is it with a check on one of my calculators or PDAs.
Because of some unfortunate events I had to put both 28S in storage two years ago, with batteries. Last weekend I got them out of storage and checked them. Fortunately, the batteries did not leak and the battery compartment was intact. Then I checked the clock. It was fifteen minutes past the current time on one of the calculators, and fourteen minutes before on the other. Other than this, the two 28S were fine and now have new batteries.
I have checked about the accuracy of the program on the documentation I have but there is not much. Does anybody have any experience on this?
Thanks in advance.