Handbook of Railroad Construction; For the use of American engineers. / Containing the necessary rules, tables, and formulæ for the location, construction, equipment, and management of railroads, as built in the United States.

by George L. Vose

also

eh = 75 × 13
77.6 = 12.

In the second system,

be = 30 × 62.6
90 = 21,

also

eh = 60 × 20
62.6 = 20.

In the third system,

be = 45 × 48.5
90 = 24,

also

eh = 45 × 24
48.5 = 23,