(06-29-2018, 02:35 PM)BigBill Wrote: Diagrams would sure help in a discussion like this. :)
https://en.wikisource.org/wiki/File:APN2...e2603b.png
This example is 40 north or south (from American Practical Navigator), however, i always start with drawing the center horizontal and vertical lines at the center of the page - it gives me a better frame of reference, then the circle is added with the aid of a circle drawing tool (adjustable compass), but the following directions are good too.
Step one: At the center of the sheet draw a circle with a radius equal to 1° (or any other convenient unit) of latitude at the desired scale. If a sheet with a compass rose is available, as in Figure 2603b, the compass rose can be used as the circle and will prove useful for measuring directions. It need not limit the scale of the chart, as an additional concentric circle can be drawn, and desired graduations extended to it.
Step two: Draw horizontal lines through the center of the circle and tangent at the top and bottom. These are parallels of latitude; label them accordingly, at the selected interval (as every 1°, 30', etc.).
Step three: From the center of the circle draw a line making an angle with the horizontal equal to the mid-latitude. In Figure 2603b this angle is 40°.
Step four: Draw in and label the meridians. The first is a vertical line through the center of the circle. The second is a vertical line through the intersection of the oblique line and the circle. Additional meridians are drawn the same distance apart as the first two.
Step five: Graduate the oblique line into convenient units. If 1' is selected, this scale serves as a latitude and mile scale. It can also be used as a longitude scale by measuring horizontally from a meridian, instead of obliquely along the line.
(Steps four and five also apply to printed plotting sheets)