How can I safely and effectively use pressure canning to preserve diced tomatoes?

To safely and effectively use pressure canning to preserve diced tomatoes, follow these steps:

1. Wash and dice fresh tomatoes.
2. Fill clean canning jars with diced tomatoes, leaving proper headspace.
3. Add lemon juice or citric acid to each jar to ensure proper acidity.
4. Wipe jar rims, place lids and rings, and tighten.
5. Process jars in a pressure canner according to recommended time and pressure for your altitude.
6. Allow jars to cool, check seals, and store in a cool, dark place.