Studied from its original page
Abaque hexagonal à échelles multiples
hexagonal abacus with multiple (binary, ternary) scales · abaque hexagonal à glissement (the sliding variant, §53) · Lallemand's compass-deviation abacus for the ship le Triomphe
- Made by
- Charles Lallemand (reported and systematised by Maurice d'Ocagne)
- Year
- 1885
- Field
- Nomograms and computing charts
- Kind
- Computing chart
- Room
- Charts that compute
What it shows
A ship's compass error worked out on paper: a hexagonal chart whose scales are themselves small charts, nested level by level.
How it is read
Start at the ship's position and heading, follow the lines from one net to the next, and read the error where the last index cuts the scale.
See the original page — fig. 65, printed p. 153 (archive leaf n176)
Published 1921 (A) and both d'Ocagne and Lallemand died in 1938, so life+70 ended in 2008 (B).
The data it needs
longitude Linput · quantitative · degreelatitude linput · quantitative · degreecompass heading ζinput · angle · degreem(L, l), n(L, l)intermediate, read from observed magnetic maps and never printed as a number · auxiliaryA, B, Cper-ship parameter fixed when the chart is drawn · constant · degreedeviation δoutput · quantitative · degree
Built in 6 steps, as its maker described
ch. III part II, §§53–56, pp. 138–155; compass-deviation example §56 pp. 151–155, fig. 65 p. 153
3 other forms share this skeleton
Source
d'Ocagne 1921, Traité de nomographie, 2e éd., fig. 65
Attribution checked against the source