The received history of clock development assumes that commercially available pendulum clocks became available from 1658, based on Fromanteel's advertisments of that year offering these 'new style' clocks. But I have just read a fascinating article in th September issue of Antiquarian Horology that argues pendulum clocks were in existence considerably before then, and that the offered innovation in 1658 refers not to the pendulum but to the pendulum crutch (an innovation that improved timekeeping by allowing the pendulum some independence from the escapement arbor). I must say that I find the article persuasive but am no expert on this subject. If anyone else has read the piece, I'd be interested in your opinion of the thesis. The idea of overturing the revered 1658 date is, for sure, a startling and attention-grabbing thesis! Anyway, just thought I'd throw this out.