This is a good example of a 600 mm Japanese slide rule from about 1960.
Japan's slide rule manufacturing industry started as a result of a visit in 1894 to Europe by two Japanese engineers to look at European industry. They brought back information about the French Mannheim design and they explored various materials, in particular bamboo for slide rules. In 1895 they started the Hemmi Keisanjaku (Sun) manufacturing company, which became one of the largest slide rule manufacturers in the world. The first Sun patents were for a bamboo Mannheim (France) type slide rule. Hemmi also adopted systems Rietz and Darmstadt for its double-sided 'Duplex' scale design.
For a number of years the Hemmi cursor design left the frame open on the left, so that the right hand which moved the cursor did not cover the window (this would give left hand users a problem!)