Other than that as features, well just look at the picture below or try the demo on the side bar (although that won’t be there long). Every button you see works.
As a note though, the MR button records whatever is on the display, M+ and M- scroll through old saved values and MC clears them all. The values are stored on a cookie so it will work between sessions. Oh and the text you see under the display is customizable.
Sidebar Calculator Widget