The plating of the penny, 1840-1864 a tabulation of the measured positions of the check-letters and other relevant data arranged for easy plate identification 
Brown, Roland.
Fisher, Harold W.(Harold Wolf),1903-
Great Britain Philatelic Society.
London Great Britain Philatelic Society,
1972
Alphabet comparator and line-engraved plating gauge in pocket
Bibliographyp.156
Postage stamps
Postage-stamp printing.