What is the Digrafid Cipher?

In the digrafid cipher, a mixed alphabet is written into a 3x9 grid, and a second mixed alphabet is written into a 9x3 grid. A 3x3 grid of numbers is written to the right of the first mixed alphabet grid, and the second mixed alphabet grid is written below the 3x3 grid. The first mixed alphabet grid has the numbers 1-9 written at the heads of the columns. The second alphabet grid has those numbers written along the right. A fractionation is chosen. The plaintext is written in groups of two. A unique three-digit number is found for each digraph. The digits are grouped by the fractionation (a fractionation of three consists of three digraphs per group), and then the numbers are read horizontally by group to determine the ciphertext digraphs.

Example

First Mixed Alphabet Keyword: kaatskill
Second Mixed Alphabet Keyword: mountains

Tableau

1 2 3 4 5 6 7 8 9
K A T S I L B C D 1 2 3
E F G H J M N O P 4 5 6
Q R U V W X Y Z # 7 8 9
                  m c p 1
                  o d q 2
                  u e r 3
                  n f v 4
                  t g w 5
                  a h x 6
                  i j y 7
                  s k z 8
                  b l # 9

Plaintext: RIPVANWINKLE

Fractionation: 4

Encipher steps:

Ri Pv An Wi  Nk Le
2  9  2  5   7  6
7  6  1  7   5  2
7  4  4  7   8  3

CT: 292 576 177 477 765 283
CT: Rq  Wa  Qi  Vi  Nw  Re

CT: RQWAQ IVINW RE