A thermometer scale in use in the United States and England. On this scale the temperature of melting ice is 32°; that of condensing steam is 212°; the degrees are all of equal length. Its use is indicated by the letter F., as 180° F. To convert its readings into centigrade, subtract 32 and multiply by 5/9. (b) To convert centigrade into F. multiply by 9/5 and add 32. Thus 180° F. = ((180-32) * 5/9)° C. = 82.2° C. Again 180° C. = (180 * 9/5) + 32 = 324° F. [Transcribers note: 180° C. = (180 * 9/5) + 32 = 356° F. ] The additions and subtractions must be algebraic in all cases. Thus when the degrees are minus or below zero the rules for conversion might be put thus: To convert degrees F. below zero into centigrade to the number of degrees F. add 32, multiply by 5/9 and place a minus sign (-) before it. (b) To convert degrees centigrade below zero into Fahrenheit, multiply the number of degrees by 9/5, subtract from 32 if smaller; if greater than 32 subtract 32 therefrom, and prefix a minus sign, thus: -10° C. = 32 - (10 * 9/5) = 14°. Again, -30°C. = (30 * 9/5) - 32 = 22 = -22° F.