The Schlage Everest Primus is the replacement for the original Primus. It combines the benefits of the original Primus system (like the sidebar and pivoting finger pins) along with the patent protected keyways of the Everest. This lock was made to extent the patent protection for Schlage's Primus line.
The Everest Primus operates much like most other pin-tumbler locks with sidebars, but the Everest Primus has one unique feature. The feature is sidebar pins that rotate. This rotation is accomplished by unevenly spacing the sidebar cuts on the key. The cuts on the key are pictured below. Notice how they are unevenly spaced.
The cutaway of the Everest Primus allows you to see the rotation of the finger pins.
In the photo below, the rotations are drawn in.
The keys of the Everest and Everest Primus are very similar. Below is a photo of the keys from the Everest and Everest Primus. They both have the C123 keyway.
The shapes are the same, but the Everest's key has a bit of a lighter colour, different patent numbers, and the "SCHLAGE" doesn't pop out at you as much.
The "SAMPLE" mark on the Everest Primus's key is because the key is for a cutaway lock.
If you've ever wondered what that little nick out of the key is for on the Everest's key is, I will tell you. The nick is to prevent an Everest blank being modified to fit an Everest Primus system. Intellegent, huh? While thinking about that, I wondered if you could have a large masterkey system with both Everest and Everest Primus locks in it. I think it could work as long as the cut for the finger pin is still present on the Everest Primus keys.