The "Download Now" link directs you to the iTunes App Store, where you must continue the download process. You must have iTunes installed in order to open the link, and you must have an active iTunes account to download the application. This download may not be available in some countries.
From KingBolt Software:
A-Z Calculator HD free is easy-to-use calculator on your iPad. This new product combines powerful calculation algorithm with user-friendly interfaces. You can easily touch the keys in the same order as the actual equation and copy equations and calculation results between 2 displays. FEATURES:24 digits X 3 lines X 2 displaysTouch display to select from 2 displaysTouch the keys in the same order as the actual equation[EXE] key to calculate your equationTouch and move between 2 displays to copy equations and calculation resultsPowerful syntax analysis and display error locationAlmost unlimited equation length15 digits calculation results (Double precision)Last answer memory ([Ans] key)26 memories you can assign the value ([A]-[Z] keys)Multiple equations with [:] and chain calculationMulti-Line playback (16 equations for each displays)Automatically insert [x] based on formula analysis[AC] key to erase selected display[Bs] key to erase 1 left characterAfter calculation, [Up] or [Down] key to call and select from 16 playback equationsAfter calculation, [Left] or [Right] key to call previous playback equation and select cursor location