Measuring Distances by Sighting with the Eyes
Proportional range-finding along two lines of sight, one diagram labeled the sun
A long horizontal strip is filled with sighting diagrams: small drawn eyes send out converging lines across the sheet, and faint architectural forms (arches and a domed building) appear in the middle distance as the objects being sighted. Three short procedures explain how to gauge an inaccessible distance or height by comparing how many times one lettered segment fits into another along the lines of sight, taking one reading with the lower eye and one with the upper. One diagram is labeled 'sole' (sun).
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Proportional sighting with two eyes (m p, a f n, b g, c o d, q h)
If a n goes 3 times into f b, then m p does the same into p g. Then draw yourself back until c d goes twice into a n; the distance from p g will equal that from g h. And as much as d c goes into o q, so m p goes into h p.
Taking the reading with the lower then the upper eye (f S, b, a o, c m, n)
Begin with the line m f using the lower eye; then raise yourself and repeat with the line n f. Then work with the upper eye and check the two sightings on the ground, in m n; and as much as c m goes into m n, so n m goes into n S.
Measuring by the sun without moving (sole, a c, m n S, o, p)
Measure without shifting your position: as much as m n goes into m S, so o p goes into p c.
Distant buildings as the sighting targets
Faintly drawn arches and a domed structure occupy the middle of the strip, standing for the distant built objects whose range and height the sighting method is meant to measure.