Black Bottom Tomatoes?

Greetings to all, This is probably such an elementary question that many of you will laugh at my ignorance but I would like some advice concerning tomatoes with rotten bottoms. I have heard that this syndrome is caused by uneven watering and I have also heard that it is caused by a deficiency of calcium in the soil. Perhaps some of you experienced gardeners wouldn't mind shedding some light on my problem. My tomatoes are in raised beds and the soil is a home-made mix of well composted yard debris, earth, well rotted chicken poop, agricultural lime and bone meal. The soil is covered with about two inches of one year old mint compost. Please reply directly to my e-mail address as I don't check the news group with much regularity. Thank you, Gary
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