Ciao all-
The experts tell me that tomato plants can't uptake calcium easily, so if blossom end rot is something you're concerned about, it's best to work on the consistent watering aspect to resolve it. Paste tomatoes are particularly prone to this, but it's not usually something that is going to knock out the bulk of your harvest. I've noticed that in my garden, if I see it, it's usually the very first fruits of the season, before the roots get really established and then it goes away all on its own.