Slide rule, navigation or gun laying, closed frame, single-sided, double-sided slide, brass / glass, maker unknown, Japan, 1920s
Slide rule, Japanese navigation or gun laying, closed frame, single-sided, double-sided slide, solid brass with brass rimmed glass cursor. With 28cm rule on top bevelled edge and 5:1 scale mm rule on squared bottom edge. In leather holster case with felt lining.
Scale markings in simplified Kanji, no maker's marks.
Stock, upper: log scale 1 - 10,000
Slide, obverse: log scale 1 - 10,000, map scale conversions: 1/16, 1/6400
Slide, reverse: split log scale 1 - 1600 and 1600 - 3199
Stock, lower: log scale 1 - 10,000
Apparently navigation or gunnery rule, reportedly c.1870 but possibly c.1900-WWI.
Damian Allen suggests:
Possible artillery use noting 1/6400 (mils) scale. [The] cm scale [indicates] use on map [for] cartographic survey. Possibly] 1920's Japanese +/- 10 years Meiji or Taisho.