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PENTAGON :
That part of the mechanism of the Sturgeon machine (e.g. T.52C) which
effected the combination of the patterns of the individual wheels into
seven sums each of four patterns in a manner capable of being
diagrammatically represented by a pentagon and its five diagonals,
the sides being lettered a, b, c, d, e, starting from apex No. 1.
and preceding clockwise and the diagonals f, g, h, i, j, similarly,
and the sixth and seventh sum being obtained from the diagonals
alone by omitting the second and the fourth respectively.
PERIOD :
Interval at which any cyclic series repeats; e.g. the length of a
recurring key, or of any component part (i.e. wheel) of a machine-key;
the width on which transposition is applied; the width on which an
analysis of a cipher or key is made.
PERIODIC :
Characterized by periods; recurring cyclically.
P/F :
PHONETIC :
(of groups, esp, call-sign groups). Pronounceable.
PICTURE FRAME :
Type of transposition pattern having large rectangular block of black
squares in centre.
PILOT :
(short for Pilot-balloon observation). A message containing observations
of wind-speed and direction at successive levels in the upper atmosphere
above a particular Met. station at a particular time.
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