The download button opens the iTunes App Store, where you
may continue the download process. You must have iTunes installed with an
active iTunes account in order to download and install the software. This
download may not be available in some countries.
You move SLIDER in this App, and you'll understand trigonometric function. At high school, when you solve a trigonometric equation (or inequality), you don't need to draw a circle figure by using this App. Furthermore, you will understand why "sin(x+pi/2)=cosx" by moving a graph of sinx. (MADE IN JAPAN)