This is a specimen of the manner in which sea charts are commonly drawn, by help of the sides of a regular poligon, shewing the points of the compass card. The corners of the poligon being joined, do become the points &amp; subdivisions of the compass.<br><p>Single sheet, engraving. Scale [circa 1:3,000,000]. The scale is in leagues.This is an ungraduated chart with rhumb lines. Soundings, rocks and sandbanks are shown. 
</p><p>A page from an unidentified instruction manual.<br></p>
G223:1/47 specimen chart, anon
<div class="fn value">
<span lang="en">Anonymous</span><span style="display:none">Unknown author</span></div>
18th century?
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