The format is 
ZZ NNNNN
[]
Reliability tests were performed to check the coherence between
the zones of the DM (BD, CD, and CPD) numbers and the declination at the epoch
of the catalogue (1855 for BD, 1875 for CD and CPD), and also to check that
the numbers increased with increasing right ascension at the epoch of
the catalogue. Resulting corrections (from typing errors in the numbers
or in the coordinates, originating from the source catalogue themselves
or from an intermediate transcription, or confusion between the CD and
CPD identifiers) have been included in the Hipparcos Input Catalogue.