An illustration showing a model that illustrates the following relationships: a:b = c:d, ad = bc. Product of the means equals the product of the extremes.
Albert A. Hopkins Scientific America: Handy Book Of Facts And Formulas (New York: Munn & Co., Inc., 1918) 41
2400×1753, 218.8 KiB
1024×747, 27.8 KiB
640×467, 17.1 KiB
320×233, 7.3 KiB