Sight Reduction Method

The intercept method of sight reduction (the New Navigation) has been known since 1875. This is a universal method, yet well into the 20th century varous other methods were used. On the page I will attempt to document these methods.

(Right) Brent's Ex-Meridian tables, tenth editon 1923, described an interesting Double Altitude method. The first sight was worked as a Sumner; the second as an intercept. Why not both as intercepts I do not know.

Brent cover.



Decide Method

There are many ways in which the observed data can be used:

  • Noon Sight for Latitude
  • Ex-Meridian sight for Latitude
  • Equal altitudes for Longitude
  • Longitude by Chronometer (a form of Time Sight)
  • Time sights with position determined by Sumner Lines.
  • Double Chronometer for Latitude and Longitude - time sights.
  • Marc St Hilaire Intercept method - known as the New Navigation.
  • Double Altitudes. Various methods, includung mixing Sumner lines and the intercept method (aka New Navigation).
  • Intersecting circles of equal altitude.
  • Lunar for time and longitude

Last Updated: Saturday 13th 2016

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