Whyte notation
The Whyte notation for classifying steam locomotives by wheel arrangement was devised by Frederick Methvan Whyte, and came into use in the early twentieth century following a December 1900 editorial in "American Engineer and Railroad Journal". The notation counts the number of leading wheels, then the number of driving wheels, and finally the number of trailing wheels, groups of numbers being separated by dashes. Other classification schemes, like UIC classification and the French, Turkish and Swiss systems for steam locomotives, count axles rather than wheels.
Northern Pacific Railway locomotives
Below is a table of information for the Northern Pacific Railway’s steam roster with a symbol, Whyte notation, common name and notes. (The notes were compiled by Richard Boyland and Wes Barris and first posted May 30, 1991, to the electronic newsgroup "rec.railroad".) Included is a breakdown of the Northern Pacific classes, along with the date of their first construction (when known), builder, and road numbers.