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.
From Cheng Bin:
The App is a collection of 4 kinds of measurement tools. Through this App your devices can turn into a ruler, a protractor, a level or a compass. You can use it in many cases, which is simple and practical.Ruler: Proportion of 1:1 . A positioning pointer is included in the ruler for measuring , with which the App can directly read the value.Protractor: A standard protractor, which also includes a positioning pointer for measuring. When the rear camera is focusing on something, you can read the angle by adjusting the angle of positioning pointer pointing which is accomplished by button.Level: A simulation bubble level. Putting your device on a plane, the App can directly read the levelness.Compass: A beautiful compass. Its red finger always points to the north.