Pressure canning at odd pressures
I just spoke with someone from Presto - apparently, the pressure is meant to be maintained by adjusting the heat source, and the weight provided with the canner is meant only to build pressure and not as a regulator. They also recommend against adjusting the weight in order to achieve in-between pressures. Not sure why on that last point - I'll follow up here with more info when I hear back from them.

They also sent me a separate recipe book meant to be used with the variable weight and I found that all of the 6 lb recipes are the same when used with the 5 lb weight.  And likewise, the 11 lb recipes are the same when used with the 10 lb weight. My best guess is that they are adding 1 lb to the recipes for use with the dial gauge to err on the side of safety, whereas the weight holds a more consistent and predictable amount of pressure.

UPDATE: Spoke with another rep at Presto who indicated that because there is a certain margin of error with the gauge that it would be unsafe to calibrate a weight by reading the gauge. I personally feel that you should be able to logically deduce the achieved pressure with a bit of trial and error using known weights, but I can understand the importance of safety and accuracy when it comes to knowing what pressure you are dealing with.