In the mid 1950’s, Buddy Emmons contributed to the evolution of the pedal steel guitar by splitting the function of the two pedals that changed the pitch of several strings from the I chord to IV chord. This “split-pedal” setup became the standard pedal arrangement in the E9 tuning, since it allows greater musical flexibility than the earlier pedal setup pioneered by Bud Isaacs. Buddy also expanded the tuning from 8 to 10 strings, adding the first two so-called “chromatic” strings.
His copedent evolved over the years, including experiments with 12-string necks tuned to E13th. Most sources agree with the basic arrangement in the chart shown below for his D-10 instruments. It’s very typical of how most new guitars are configured today, except for the lack of a 1st string raise on RKL.
See also: Buddy Emmons’ C6th Copedent