This is an incomplete example (the arms are missing) of an unusual 4-armed instrument. The needle rim is graduated to 30 minutes. The variation scale, at south, extends ± 20 degrees, and is read by vernier to single minutes.
Francis Arnold was an immigrant from Franfurt who signed naturalization papers in Philadelphia in 1854. He worked briefly for William J. Young, and then went into business on his own, advertising as a manufacturer of surveying and engineering instruments. He settled in Chicago around 1860. By 1875, B.
Kratzenstein was advertising as Successor to F. Arnold & Co.