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Slide Rule

Drag the slide (middle) left/right

Drag the cursor (red hairline)

Scroll to zoom in/out

Reading

Cursor on D:1.000
Cursor on C:1.000
C × D index:1.000
Cursor on A:1.000
Cursor on CI:1.000
Cursor on L:0.000
Cursor on S:--

The Slide Rule

Invented by William Oughtred in 1622, the slide rule uses logarithmic scales to turn multiplication into addition. Sliding the C scale so its 1 aligns with a number on D, then reading the cursor on C, gives the product on D.

Scales: D/C = multiply/divide, A/B = squares, CI = inverse C, L = log10, S = sine, T = tangent