If you have a Presto pressure canner you should have your gauge tested yearly. Marisa is available at the MNVC office today until 5:30 and Saturday from 1:00-2:00 or during down time during other canning workshops to test your dial gauge.
Your All-American canners dial gauge do not need testing as they also have the weighted gauge which should be the one you go by when canning.

Marisa also has a lot of other resource information on hand if you want to come ask questions or get additional information.