I copied and pasted this from another gal who wrote a review on Amazon.com. She says exactly what Presto told me, too ! ................... Even though there is a dial gauge, you actually CAN use this canner as a weighted gauge canner! I contacted Presto about this, and the weight that comes with this canner is the same weight that is on their smaller pressure cookers, the 4- and 6-quart models, which cook at 15 PSI. Therefore, when the weight begins to gently rock, it is pressure canning at 15 PSI. However, people who live below 1,000 feet of elevation need to pressure can at 10 PSI, so you either need to make sure your gauge is accurate, or you can purchase a 3-piece pressure regulator from Presto (model #50332). The lady at Presto confirmed that by using this particular pressure regulator, it will then effectively be a weighted gauge canner with the dial there just for reference. Now that I have a way to pressure can using just a weighted gauge and not depending on accuracy of a dial, I love this canner. I do not have a way to have my gauge checked other than by sending it to Presto, and that takes weeks to have it checked. Also, I don't know how accurate the gauge would be after being in the mail getting jostled around. .............................. I wish I could find the other link I used for the part, it specifically said for CANNERS, and not just cookers. Plus, Presto makes a new canner, sold at Walmart, that is only a weighted gauge canner. There is also a link to one of the extension sites that says that on Presto, the weight should rock gently the whole time, not so many times a minute. Here is a link that might be useful: Three piece weight set.

This is the bottom of the 18 qt, but it's the same. 8 inch raised section fits well on glass or coil round burner, not sure how it will be on your 6 inch (square). It will fit, but depending on how close the center of that burner is to the edge of the stove it will overhang just like your 14" stockpot does. I can't speak to whether you could set this centered between the burners which you said span 15" - it might not be stable and I don't know how 2 flames on the sides (lapping up the sides? Unless you can control just the left or right ring of each burner - I saw a camp stove like that, might have been at Northern Tool or Amazon) and cool spot in the middle would affect function, or whether it would warp. Be sure to ask the rep tomorrow.

Of all the home canners I know I can honestly say none of us would try to process 19 quarts of anything all at one time much less 24 or 28 quarts. They would break it down into 3 separate batches over a couple of days or use multiple canners as long as the heat source is available. Wife and I often run 2 23 qt canners but at staggered times. First because if using a mixed recipe it would mean tripling or more the recipe which isn't recommended because of the mistakes in measuring that are often made, second because it would require using huge commercial prep pots and pans, third because unless they had a multiple man assembly line there is no way you could get the hot jars filled and into the canner all at the same time so many would be sitting cooling on the counter while others were sitting in the hot canner waiting for it to get filled and started, fourth because the weight of said filled canner would be almost impossible to lift and require a heavy duty special burner or commercial stove of some kind, fifth because it would take a canner that big so long to come up to pressure and so long to cool down you could do 2 regular batches in the same time, etc. Just some thoughts to consider when making your decision. :) Personally, if you have available multiple heat sources then running 2 canners, filling the second while the first gets started running so the second goes on about 1/2 through the first run, is easy. That over-lapping approach works well. Dave

If the 21qt is new, it is very possible that the two canners are made from different material and the 16qt retains heat longer. As long as it maintained pressure the entire time, I don't think you have anything to worry about. At first glance, I would have thought there was a gasket issue but not at all. I just think the 16qt is of sturdier material and holds on to the heat. Happy canning!