Buckinghamshire CC ANPR cameras
colinthomson1 at o2.co.uk
Thu Feb 9 11:42:09 GMT 2012
>  No idea where this comes from, it's not sufficiently close to 2.5"
> for example, and if metric why not 60mm?
> Roland Perry
Maybe it comes from a fifth of a foot? It's very close to that (much closer than 60 mm or 62 mm).
But looking for a meaning for 61mm may be a bit pointless as the statutory instrument specifies, for plates fitted on or after 1 Sep 2001, a character width of 50mm and inter-character spacing of 11mm, which was derived from the previous 57mm and 11mm by producing a condensed version of the font. Condensation was needed because registration marks were longer than previously - which also caused the previous option of a larger face (89mm height instead of 79mm, 64mm width instead of 57mm, 13mm inter-character space instead of 11mm, and 38mm inter-group space instead of 33mm) to be dropped altogether. So 61mm appears to be an accident arising from the condensation, not a figure derived from a previous regulation which used inches. I think the 1971 regulation used metric too, and while 68mm doesn't look like anything derived from an earlier non-metric number, 64mm and 13mm may come from 2.5in and 0.5in; 57mm could come from 2.25in, but I can't think of anything that 11mm could have come from - unless maybe someone decided to use 11 instead of 12 (for 0.45in, 11.7cm, which is where a 2.5in to 2.25in scaling would have put the 0.5in gap on the smaller option) because 12 was too close to 13.
More information about the ukcrypto