Can anyone tell me what is wrong with my tomatoes?

The tomatoes on one of my plants are all looking like this on the bottoms. I was hoping one of you Texas tomato growers could tell me what is wrong with it.

It's called blossom end rot.
http://vegetablemdonline.ppath.cornell.edu/factsheets/Tomato_BlossRt.htmhttp://www.veggiegardener.com/preventing-blossom-end-rot-in-tomatoes/

I supposed that by now you have learned that it is a lack of calcium that causes this and that you can correct this by the use of a common product sold in garden centers ..if I have any blossum end rot I just crumble up some sheetrock as Gypsum is the main ingediant in sheetrock and it is simply calcium sulfate seems to work okay and is mostly free or you can buy agri gyp or garden gypsum

I tried egg shells last year and it worked very well too.