I have a pressure canner. You can use it as a pressure cooker if you want to, it won't hurt anything. You actually can pressure can in some pressure cookers, but most are too small for quart or larger jars. Also, you need one that will maintain the same pressure for a long period, and many cookers fluctuate too much, causing poor seals. But the largest difference is just the size. Canners are bigger than cookers because you might want to can gallons of tomato juice, but most people do not need to pressure cook beans for 100 people at a time.
I choose to use a dial gauge because I can at altitude, which means I need to can at higher pressure than standard, so a weighted gauge would actually be too cool for proper sterilization. If you are less than 3500 feet above sea level it won't matter, but higher than that it does. Some weighted ones co,e with weights that vary so you could, in theory choose a heigher weight and get the right pressure/temp, but the scientist in me likes the gauge. I actually have never calibrated it, but I can above the recommended pressure anyway so I'm not on the boarder of safety.
I LOVE my pressure canner for tomatoes, heirlooms in particular. Their sweet flavor really shines when you don't have to add acid. Good luck and HTH.
