Financial calculators puzzle

[dm319]

The Busicom FN400 seems to have 13 digit accuracy, and it actually does pretty well, returning results on average better than most financial calculators - even the top HP ones.

The Busicom FN200 does pretty badly. It has 12 digits accuracy, but its results are at the bottom end of the results table, only just beating the original HP-27 overall.

Results are here, which is a central place to put them for the moment, but I'm running out of space editing that first post in the thread. I haven't quite updated it yet, but I'll put in a 'digit efficiency' graph at the end.