How to test for setting point
There are a few different ways to test for setting point but I favour the low-tech saucer method:
When I start making the jam, I pop a saucer in the fridge to chill. When you think the jam might be ready, put a blob of jam on the chilled saucer, leave for a moment, then gently push with your finger. If the surface of the jam wrinkles the jam is ready to be potted.
As simple as that!