ATX also stands for Austrian Traded Index, the official index of the Vienna Stock Exchange (Wiener Börse AG), similar to the Dow Jones. Its constituents are 22 different companies continously traded on the Vienna Stock Exchange.

It's construction principle is capitalization-weighted value ratio. (Whatever that means)

Base date: January 2, 1991
Base value: 1,000.00
Interval of calculation: Real time


source:
http://www.finix.at/fin/atx_box.html