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Hall & Watts Defence Optics Ltd. SM1 MkV Pilot Balloon Theodolite
The model SM1 MkV Pilot Balloon Theodolite is a fifth generation instrument from a line of Theodolites that dates back to 1936 with the original Meteorological Office Pattern Theodolite Specification and the introduction of the E. R. Watts Mk I Pilot Balloon Theodolite. The Mk V instrument is built to meet the current specifications of the United Kingdom Meteorological Service and the World Meteorological Organization (WMO).
Distinguishing features of the Mk V theodolite are the use of a Pentagonal Prism in the bent axis telescope, which allows for better stability of the optical alignment, a closed circle design for durability, two levels of magnification offering wide and narrow fields of view (accomplished with a switchable finder scope using the same eyepiece with two objectives) and a lined gradicule supporting the tail method of altitude determination.
The placement of the azimuth and elevation circles directly above each other as well as the use of Micrometer drums facilitates rapid determination of azimuth and elevation directly to the 10th of a degree.