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Alan,

The sextant is a Chas Hutchinson model from around the early 1900s. Actually it is smaller and lighter than a Tamaya or Plath.  The index arm operation is quit different than a modern sextant using friction clamps to secure the arc position. There is a magnifying glass on the index arm for reading of the vernier scale. Precision is to only 1'. The x3 optic is pretty good. Filtering is just ok but good enough. 

http://www.skipjackmarinegallery.com/late-19th-century-brass-sextant-made-for-chas-c-hutchinson-boston-nautical-instruments-company.html

Greg Rudzinski