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Hemmi/"Sun" Model 250

• Type: Trig Duplex
• Size: 10 Inches / 25 cm
• Material: Bamboo and celluloid
• Scales:
  • Front: K A [ B TI₂ TI₁ SI ] D DI
  • Back: DF [ CF CIF CI C ] D L
• HvH: 3388

A basic trig duplex slide rule, with some notable differences in the scales. First, the sine and tangent scales are inverted and read against the DI scale. I wonder if this is some sort of transitional model for users migrating from mannheim rules to duplex rules. If you set the angle against the D scale's right index, you can read the sine or tangent on the D scale. There are two tangent scales, one for angles less than 45 degrees, one for more than 45 degrees.

The folded scales, CF and DF, break at the square root of 10 rather than at pi. The designer is onto the idea that a folded scale can save time in setting scales, but he seems to have missed the opportunity to provide instant multiplication and division by pi.

Dated March 1957 ("HC" mark on upper stator)