Meridians: Equally spaced straight parallel lines.
Parallels: Unequally spaced straight parallel lines, perpendicular to the meridians. Spacing is closest near the poles.
Poles: Straight lines equal in length to the Equator.
Symmetry: About any meridian or the Equator.
This is an orthographic projection onto a cylinder secant at the 50º parallels. It is equal-area, but distortion of shape increases with distance from the standard parallels. Scale is true along the standard parallels and constant between two parallels equidistant from the Equator. This projection is not equidistant.
For cylindrical projections, only one standard parallel is specified. The other standard parallel is the same latitude with the opposite sign. For this projection, the standard parallel is by definition fixed at 50º.
The Balthasart Cylindrical projection was presented in 1935 and is a special form of the Equal-Area Cylindrical projection secant at 50ºN and S.