Drag Racing Results - DA calculator?

OK, here is a stupid question: What does DA stand for, and how do I calculate it? I know its some kind of drag racing correction factor based on weather, but thats it.

Thanks.

Density Altitude/Altitude Density however you want to say it.

Here's a decent calculator I stumbled on with a little explaination.

http://wahiduddin.net/calc/calc_da.htm