File:Stirrup method (1652)-(7).svg

Summary

Ozanam's method (1673) and later Mayall (1973), and others. It works well in higher latitudes requiring a narrower sheet of paper.

• Take a large sheet of paper (Two times wide as high for 52 N).
• Starting at the bottom, draw a line across, and a vertical one up the centre. Where they cross is important call it O.
• Choose the size of the dial, and draw a line across. Where it crosses the centre line is important call it F
• You know your latitude. Draw a line upwards from O at this angle, this is a construction line.
• Using a square, (drop a line) draw a line from F through the construction line so they cross at right angles. Call that point E, it is important. To be precise it is the line FE that is important as it is length Failed to parse (Missing <code>texvc</code> executable. Please see math/README to configure.): <semantics><mrow class="MJX-TeXAtom-ORD"><mstyle displaystyle="true" scriptlevel="0"><mi>sin</mi><mo>⁡<!-- &#8289; --></mo><mi>ϕ<!-- &#981; --></mi></mstyle></mrow><annotation encoding="application/x-tex">{\displaystyle \sin \phi }</annotation></semantics> <img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/fc867c18657f81cf14e9381bb8603ea969d63566" class="mwe-math-fallback-image-inline mw-math-element" aria-hidden="true" style="vertical-align: -0.671ex; width:4.67ex; height:2.509ex;" alt="{\displaystyle \sin \phi }">.
• Using compasses, or dividers the length FE is copied upwards in the centre line from F. The new point is called G and yes it is important- the construction lines and FE can now be erased.
• From G a series of lines, 15° apart are drawn for 9, 10, 11 and 1, 2 and 3. A vertical line is dropped from 3.
• A diagonal DW is drawn . From the 2 point, a line is dropped orthogonally to the diagonal. This point is called L. (similar procedure for K) Stirrup then moved his set compasses down the diagonal till he found the point N, a line right-angles to the diagonal and an exact length to the vertical. This point is the 4 marker.
• The 4 hour line is drawn from here to the origin.
• The values before and after 6 are calculated through symmetry.

Licensing

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