Protractors are distributed in the form of a .sit file (a Stuffit Archive) called TrilithonProtractors.sit. When you have downloaded the TrilithonProtractors.sit to your desktop, you will need to Unstuff the file to obtain its contents. Unstuff can be done by using StuffIt Expander from Aladdin Systems.

Download StuffIt Expander from Aladdin Systems

StuffIt Expander will extract the contents of TrilithonProtractors.sit, which is a Disk Image package (a .dmg file). TrilithonProtractors.dmg should appear on your desktop with the name TrilithonProtractors.dmg, and will be mounted automatically, appearing on your desktop as a removeable disk icon. Double-click on the mounted disk icon to open the Protractors distribution package.

Drag the Protractors application to your preferred applications folder, usually Applications in your home folder.