The body support limb can rotate 180°.
Conventional position of the body tube is fixed by a locating pin.
Locating pin underneath the support limb sets the rotational position of the microscope body.
Horizontal position for high magnification imaging. When placed in front of a light source this position would illuminate the sample with the most light.
Woodcut from Lobb, EG. 1866. Note on illuminating objects with high powers. J. Microscopical Sci. p. 39.