Call numbers in the Cutter Expansive Classification consist of letters, numbers and punctuation. To put two call numbers in order, they are compared character by character, from left to right, using the five rules given below. The order of the call numbers is determined by the first pair of characters which are not equivalent according to these rules.

The first three rules govern comparisons between characters of the same type.

  1. Pairs of letters are compared alphabetically. A comes before B, C comes before D, and so on.
  2. Pairs of digits are compared numerically. 0 comes before 1, 4 comes before 5, and so on. Resist the temptation to compare numbers of more than one digit; call numbers must always be compared character by character.  (So 13 or 158 comes before 2.)
  3. When comparing punctuation marks the period (.), plus sign (+), and parallel (∥ or //) are considered equivalent. Only one other punctuation mark is in use, the colon (:), which comes after the other marks.

The remaining rules govern comparisons between characters of different types.

  1. A punctuation mark comes before a character of any other type.
  2. A number comes before a letter unless the preceding character was a number, in which case the order is reversed. (So A4 precedes AA4a precedes AA42.)

Some examples:

H.F345a comes before H.G345a (by the first rule)

Y.G345a comes before Y.G36 (by the second rule)

ZY.G36 comes before ZY:A22.G287 (by the third rule)

G+A22 comes before G.Z99 (by the first and third rule)

W.P25 comes before WA.B32 (by the fourth rule)

W84A.B22 comes before W844.B22 (by the fifth rule)

W.9L22 comes before W.B66 (by the fifth rule)

VV41.A83 comes before VVB (by the fifth rule)