5. Use inferior figures in all chemical symbols, and omit spaces between the letters and signs.
6. Use superior figures in connection with reference letters, as A1, A2, a1, a2.
7. It is impossible to give definite rules that will govern in all cases as to what should go in figures and what should be spelled out. It is a question which must be left to the judgment of the workman. General rules which will serve as a guide to the tendency of the style follow:
Put in figures—
Distances: 50 miles; 17 yards; 8 leagues.
Clock time: 10.25 p. m.; 12 o’clock and 30 minutes; half past 9.
Weights: 12 pounds of beef; 4 hundredweight of stone; 8 centals of wheat; 2 grams of powder.
Measures: 40 bushels of wheat; 1 gallon of wine; 15 knots; 6 acres; 9 hectares.
Degrees, etc.: 17° 24′ 17″; 10° below zero; in longitude 46° west (but tenth meridian of longitude, sixth degree of latitude, etc.).
Dimensions: 16 feet square; 24 by (not x) 12 feet; 2 by 6 inch plank; 4 kilometers square.