(Also marked as 4-1/4cm and 4.25cm)
The 40/2 Biotar was not-quite a wide angle, not-quite a normal lens of high speed, but mediocre performance. It was introduced in 1933 in black and nickel . The finish was changed in 1935 to chrome. Some of the late nickel lenses and early chrome lenses have the aperture scale plated rather than painted black.
In 1936 Zeiss changed the marked focal length from 4cm to 4-1/4cm (and some of the catalogs list it as 4.25cm, although I don't think any lenses were so marked). The lens was discontinued in 1938 production was less than 400 units marked 4cm, and 250 marked 4-1/4cm.
Finders to match the lenses were made in both black and nickel, and black and chrome finish, and could be found marked with either focal length.
The less common 4-1/4cm Biotar with 4cm finder, and leather pouch for the finder.