These circular planes are fitted with flexible spring steel faces for planing
convex and concave surfaces.
The face is anchored at each end of the body, and is screw adjusted from
the centre.
The frame provides handles at both ends.
Here it is with it's sole in the Convex position.
And now, it is Concave.
Here it is Flat. It is 10" long and has a 1-3/4" cutter.
A very nice example from around 1970.