24B Page 116
(c) Garbo rectangles.
By means of the special switches (56 E), Garbo is made to print ΔZ1 + ΔZ2, as, or x, in width of 41, with plenty of spacing.
After 31 rows, i.e. after 1271 places, a dot or cross will have been printed for each cell of the rectangle. The 1272nd entry is printed immediately below the first, the 1273rd below the 2nd, and so on. Finally the scores for a particular cell of the rectangle will be a short column of dots and crosses: the excess of dot over cross for each cell is entered by hand on the Garbage, and afterwards transferred diagonally to a rectangle.
Because Garbo deltas backwards it is necessary to start at the second place of the cipher tape and correct the first entry by hand.
The method is very convenient for short texts, such as key. Its disadvantage is that if the depth, i.e. the number of places per cell, is large, adding the scores for each individual cell is laborious.
In diagonal entering each row of Garbage must obviously end in the last column of the rectangle: to aid and check entering, it is labelled with the row of the rectangle in which it should start, viz., in order, 1, 11, 21, 31, 10, 20, 30, 9, 19, 29, 8, 18, 28, 7, 17, 27, 6, 16, 26, 5, 15, 25, 4, 14, 24, 3, 13, 23, 2, 12, 22. A better plan would be to write (or have printed) Garbage row numbers against the rectangle: this has been done spasmodically for key rectangles.
For the complete system of checks see 36 G.
(d) Thurlow rectangles.
A modification of Garbo rectangles, devised for long texts to reduce the labour in finding the scores for individual cells: the idea is to represent 5 dots and crosses by a single figure.
The first step is to produce a tape on Miles, on which is punched nothing but Z1 + Z2, as dot or cross, arranged thus
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| Thurlow tapes of the first kind. |
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