From parallel waves: Designated person (who should be the end of a wave) begins Casting 1/2 with alternating hands down the wave, doing this the number of times indicated by the first number. The person initially "casted" will, after this initial cast, pick up the 2nd number and begin Casting 1/2 with alternating hands.
Examples: Head men start a Rolling Ripple 3 by 1 -- ends in a wave, 3 by 2 ends in a wave, 2 by 1 ends in a wave, 2 1/2 by 1 1/2 ends in a facing diamond, 3 by 1 1/2 ends in a facing diamond. 2 by 1/2 or 2 1/2 by 1 gives phantom setup.
This definition is from News and Notes by Al Brundage, Earl Johnston and Ed Foote.
It is provided here for informational and educational purposes only.