A surveyor’s cross is a simple instrument that is used to establish
straight lines and lay out lines at right angles to one another. There are two
forms. The open form has four arms set at right angles to one another, with an
open sight at each end. The closed form—which seems to have been introduced
around 1803 by William Jones, an instrument maker in London—is cylindrical,
with four slits at right angles to one another.
Ref: The Cyclopaedia; or, Universal Dictionary of Arts, Sciences, and
Literature, ed. Abraham Rees (London, 1819), vol. x, art. "Cross, in
Surveying."
