By George, I think I've got it! I swapped in the older, more broken-in saddle for a comfier ride, and the new computer keeps proper time. Huzzah! Except... Well... There's a reason the style of saddle I like is called a mattress saddle. As they get older they tend to squeak like a bed at a cheap motel. The noise is especially noticeable in amidst the silence of the woods along the path, and also because everything else on the bike is still so mechanically quiet. Maybe some neatsfoot oil. I must still have some in my softball bag.

The legs are in much better shape, too. I did twenty miles last night, and could've gone more. I was a little stiff this morning, but still felt good enough to do another fourteen tonight with my best time of the year. Apart from the humidity, the weather's been near perfect for riding.