Thank you for the links. Vent pipe is a must for such an upgrade. I will definitely consider the testing facility as well, however I heard that it is much cheaper to get a new gauge That's where the $50 total figure was popping out for the full upgrade.

The 11 ppi for a quart jar pork canning at 90 minutes was found from the trusted canning source, dealing with exact same canner model. The 15 pounds value is so common only because you cannot actually set the 11 ppi pressure with the weighted jiggler (it usually has only 3 fixed pressures available to set and control - 5, 10, and 15 ppi). That's why I'm on the fence about the upgrade. It's not just about the overcooking, but rather about energy saving, especially If I'll have to use a generator, propane, or a wood stove in a survival situation. Actually, it was not much of a hassle to monitor the gauge even for the first time, as it seems very stable as soon as you hit that sweet spot. If I'll find that my marking for that power output is repeatable on the next batch, then it will be a nobrainer to just set it and forget it for 90 minutes.