I had to replace the batteries today on my trusty HP15C calculator – 31 years old and as good as the day I got it. From memory its only the 4th set of batteries its needed in 31 years.

After I replaced the batteries the calculator started up in ‘complex number’ mode and I had to locate the manual to find out how to get it back to real number mode (g CF 8). For a bit of a trip down memory lane I entered and ran a simple program (iteratively display powers of 2) – something I hadn’t done for several decades.