This article is from the Food Preserving FAQ, by Eric Decker firstname.lastname@example.org with numerous contributions by others.
The instructions say the appropriate pressure is being maintained
when the weight jiggles about 4 times a minute. When I have the weight set
to 15 pounds, I cannot get this to happen. It is either jiggling almost all
the time or only 1-2 times a minute.
Two answers from two rec.food.preservers.
>From John Taylor :
Jiggling once or twice a minute is fine. It indicates that you have full
pressure in the canner, which means it's at the desired temperature. If
this is happening at a constant heat setting, it also indicates that the
temperature is not falling and then rising again (which you wouldn't want).
Sounds like you've got an appropriate setting for the flame.
>From Richard Nielsen :
I've had similar problems with a Mirro 12 qt. I finally decided to let
jiggle most of the time. I add an extra cup or two of water and I've never
had it even come close to boiling dry in a 90 min process time.