Okey, GB ... put your reading glasses and try again ...
The book doesn't say to calibrate a dial guage before each use ... it says to have the accuracy checked before each canning season
. I haven't looked at how the dial guages are made - but I think it's safe to say you're not going to have the equipment or parts to calibrate or rebuild one. All you can do is replace it if it goes wonkey on you.
As to which canner is which ... if it doesn't have a dial, and just uses weights, it's a Weighted-Guage canner. If it has a dial, then it's a Dial-Guage canner.
The Mirror lines I've seen don't have a dial guage so it is a weighted-guage ... you get a choice of 5, 10, or 15 lbs. You can find the Mirro manuals
at this site (listed as pressure cookers but it also includes the canners).
The Presto line is definately a Dial Guage canner - it only comes with a 15-lb weight so dial-guage accuracy is most critical for this one. You can find the Presto manuals
at this site.
The All American is kind of a hybred ... depending on some things it can function as either/or. If you are processing at 5, 10, or 15 lbs - then the weight is the regulator and the dial is only a reference. If you're above sea level where you really need accuracy to get the ideal temp between 11-14 lbs - then it works like a Presto and the dial needs to be accurate. But, All American's dial is gear driven and they claim it is more accurate and doesn't have to be checked every year like other brands. You can find the All American manuals
at this site (click on Continental US, then on Pressure Cookers to get to the manuals).
Personally - I like the All American best.