The Abscissae, or horizontal distances, are temperatures in degrees Fahrenheit from 30 degrees below zero, at the left, to 220 degrees above, at the right.
"Seasoning of Wood"
Joseph B. Wagner
34, however, give the furnace draft necessary to burn various kinds of coal at the combustion rates indicated by the Abscissae, for a general set of conditions.
"Steam, Its Generation and Use"
Babcock & Wilcox Co.