The rover arm holds and maneuvers the instruments. Much like a human arm, the robotic arm has flexibility through three joints: the rover's shoulder, elbow, and wrist. The arm enables a tool belt of scientist's instruments to extend, bend, and angle precisely against a rock to work as a human geologist would: grinding away layers, taking microscopic images, and analyzing the elemental composition of the rocks and soil.
At the end of the arm is a turret, shaped like a cross. This turret, a hand-like structure, holds various tools that can spin through a 350-degree turning range.
The four tools, or science instruments, on the robotic arm are:
The Microscopic Imager
The Mössbauer Spectrometer
The Rock Abrasion Tool (RAT)
The forearm also holds a small brush so that the Rock Abrasion Tool can spin against it to brush the teeth of the grinder