This is probably going to be completely boring for anyone who isn't me. But I want to write it down somewhere, so it might as well be here.
Computer totally reset in the afternoon, before my commute home.
Two balacing factors:
(Did I set it to 2070, the listed 700x18 size? I may have.)
Update, June 9th 2008: I found my gear calculator program, dating from May 20th 2007, and it uses a wheel size of 2155 mm.
At the April 14 2008 reset, I put the wheel size at 2170 mm. This appears to be roughly correct within a cm or less, based on rolling tests at work (where there is a set of 1-foot floor tiles nicely lined up).
I've now reproduced this. Once the odometer is high enough, press
and hold the left button on the second screen to change the clock;
it may matter that this was shortly after a trip reset.
(At least I assume it requires the odometer to be high enough.)