Imperforate 1840-54
perforations 1854-
perf 14 1855
14 perforations to 2cm
perf 16 1854
16 perforations to 2cm
Perf 16 started in 1854, perf 14 was introduced in 1855
Perforations were officially introduced in 1854, 14 years after the first stamp in 1840, before perforations the stamps had to be cut out of a sheet of 240 stamps using scissors. Trials on a perforating machine invented by Henry Archer were carried out between 1850-1854.
Perf 14 indicates that there are 14 perforations every two centimeters. This method was devised by Dr. Jacques Amable Legrand (1820-1912), an early French collector, who published what he called an odontometre (perforation guage) in 1866.
In England we used inches, but in France they used centimetres.
A British stamp was less than an inch high (only 24mm not 25.4mm) so it would
be difficult to count the number of perfs per inch
Eventually by 1858 most stamps were perf 14 rather than 16, I assume that this was because a sheet of stamps perf 16 was too fragile to handle compared to perf 14