Part III · The line of position · Page 2 of 3
Where the line goes: Ho against Hc
To put the line on the chart, compare two altitudes. Hc is the altitude the Sun would have if you were exactly at your DR (the intercept method module shows how to find it). Ho is what you measured.
Every minute of altitude is a mile of distance from the ground position. If Ho is bigger, you are nearer the Sun's ground position than the DR is, so the line is that many miles toward the Sun. If Ho is smaller, it is away.
Ho − Hc in minutes = miles. Ho More: Toward ("Ho Mo To").
Predict Ho is 6′ more than Hc. Which way does the line of position go from the DR?
- Sun's bearing from the DR (Zn)
- 135°
- Ho − Hc
- +6′
- So the LOP is
- 6 nm toward the Sun
- It runs
- 045°–225°
You measured the Sun higher than it would be at the DR, so you are nearer its ground position: toward.
DR N 41°12′, W 064°30′. The Sun bears 135°. Hc 38°47.3′, Ho 38°53.3′.
Ho − Hc = 6.0′: 6.0 nm toward.
From the DR, go 6.0 nm along 135°. Through that point draw the LOP, square to 135°: it runs 045°–225°.
In the practice you plot it yourself: tap the sheet to place the point, and drag it until the readout shows your direction and distance from the DR, as you would with a plotter and dividers.