If you live above 1000 feet elevation you need to figure your altitude adjustments for both water bath and pressure canning. As your altitude goes more than 1000 feet above sea level the atmospheric pressure is reduced. This causes your water to start boiling before it reaches 212 degrees.
For safety when water bath canning, your food must be heated to 212 degrees. To compensate for the temperature difference you must increase the processing time.
The pressure in a pressure canner is also affected by the same atmospheric pressure. A pressure canner needs to reach 240 degrees in order to kill the microorganisms that cause botulism. To compensate for altitude differences, you must increase the amount of pressure used. The time does not change, only the pressure used.
Therefore, as you go up in elevation you need to increase your time when using the water bath and increase your pressure when using the pressure canner.