For those who prefer plotting to mathematical calculation, the accompanying diagram will be of assistance in determining the time of Local Apparent Noon.
The method consists of plotting one line representing the local zone time of the sun’s passage across various meridians and then crossing it with another line representing the time of the ship’s crossing these meridians. The intersection of the two lines will give the time that the sun and the ship are on the same meridian.
The center horizontal line of the chart is 1200 local zone time. The center vertical line is the standard meridian. If the equation of time is zero, then the sun will cross the standard meridian at 1200 local zone time, point (a), and will cross the meridians to the east 4 minutes of time earlier for each degree east of the standard meridian (4 minutes later for west of the standard meridian as shown by line A.
Assume a time zone of +3 hours, standard meridian 45°W., date January 26, 1943, D.R. longitudes at 1130 47°-30'W. and at 1230 46°-25'W., with equation of time minus 12.5 minutes approximately.