An random orbital sander superimposes 2 movements:
a fast circular movement with radius 2-5 mm
a slow circular motion with the radius of the whole disk
This allows a lot of material to be removed without leaving too noticeable scratches in the wood. The radius of the small movement is usually determined by the design. But there are also machines with 2 different adjustable radii. A larger radius results in better stock removal but clearer grinding marks.
The following aspects should be considered when choosing a random orbital machine: