I opened the first jar last night (I'd poured the wax on the top far too thick, and couldn't break it -- I just ended up pushing it down into the bottom of the pot so that I could get at the jam!) and was a bit disconcerted to find that, although I'd tested it for setting, and in fact the top had set so firmly in the pan that I couldn't get the scum off the fruit before potting it up, the bottom of the jar, which had no fruit in it, didn't appear to have set after all.

The pot of jam turned out to be just whole fruit in thick syrup, Russian-fashion. Very tasty, but since I'd gone to the trouble of adding pectin and testing it to see if it had been boiled long enough, I was a bit taken aback!