The altitude and azimuth instruments made by Edward Troughton in London from the 1790s were remarkably stable and accurate, and Troughton & Simms continued this tradition.
Indeed, Frederick W. Simms would describe the portable Troughton & Simms instruments as being "the most generally useful of all instruments for measuring angles, being applicable to geodesical as well as astronomical purposes." This instrument, made in 1837 for Columbia College (now University), is of this sort. It has a large and powerful achromatic telescope. The horizontal and vertical circles are silvered, graduated to 5 minutes, and read by microscopes with micrometers to 5 seconds. The graduated vertical circle is counterbalanced by a second circle on the other side of the telescope. The telescope assembly and horizontal axis rest on two conical pillars, supported by wyes and friction rollers. A long level is mounted between the microscopes reading the vertical circle.
Ref: Frederick W. Simms, A Treatise on the Principal Mathematical Instruments (Baltimore, 1836), pp. 81-98.
