480
1 Stereoscopic with approximate confidence interval.
J Monocular with —
j» Binocular -■— — m—
1. Stereoscopic observation
With the aid of the Dove-prisms the y-parallax has been made appar
ently parallel to the eyebase, and observed stereoscopieally.
2. Binocular observation.
The Dove-prisms are in an ordinary position and the y-parallax is
perpendicular to the eyebase. The images are observed simultaneously
and the y-parallax is eliminated when the mark is made as distinct as
possible.