woody@rpp386.cactus.org (Woodrow Baker) (02/07/90)
This was mailed to me. The mailer could not post it. I think it is
eextremely valuable, and looks like it should end the point question.
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From: andrew yeomans <cel!ajy@relay.EU.net>
Date: Tue, 6 Feb 90 10:27:36 GMT
Message-Id: <687.9002061027@sun304.cel.uucp>
To: woody@rpp386.cactus.org
Subject: Re: Pointsizes, inches, metric
Seeing your recent discussion on point rulers, you might be interested in
the attached file. I have also been bitten by the different point sizes -
and since Crosfield's output scanners work at typical resolutions of
72 pixels per mm (and some older ones work at 72 pix/mm in one direction
and 1800 pix per inch in the other!!), the accuracy is quite important.
Our customers are in the habit of peering at the output films through
magnifying glasses. We even have to compensate for the thickness of the
film when it is wrapped around the scanner drum, as the inner circumference
is different to the outer radius (and so the operator had better load the
film with the emulsion the right side up).
Feel free to post this to News. Unfortunately our outgoing news link is
not working (:-( so I can't post it myself.
Andrew Yeomans | PSTN: 0442 230000 ext 3371
Crosfield Electronics Ltd | INTL: +44 442 230000
Three Cherry Trees Lane | Fax: 0442 232301
Hemel Hempstead | UUCP: ajy@cel.uucp or ajy@cel.co.uk
Hertfordshire | or ...!{mcvax,ukc,uunet}!cel!ajy
HP2 7RH | .. all opinions are my own, etc.
England | 'Great oafs from little icons grow' S.Fry
----------------------------cut here-------------------------------------
Point sizes
===========
The following tables give Anglo-American and Continental point sizes
according to various definitions:
Monotype et al
Monotype Corporation, and several other generally accepted sources use
1 pica = 0.1660 inch, 1 cicero = 0.1776 inch.
Monotype (rounded point)
Monotype use the rounded down value of 1 point = 0.0138330 inches
(rather than 0.0138333...) for sizes below 1 pica.
Rounded metric equiv
Sometimes the continental size of 1 point = 0.0148 inches is rounded to
1 point = 0.376 mm rather than 0.37592 mm.
MacKellar, Smiths, Jordan
MacKellar, Smiths, Jordan of Philadelphia claimed that 83 picas = 35 cm
exactly.
American Typefounders Ass
The American Typefounders Association (also Legros and Grant) defined
1 point = 0.013837 inches in 1886. However in 1959 the inch was
redefined as 25.4 mm rather than 1/0.03937 mm. If this is allowed for,
1 point = 0.0138370277 (new) inches.
TeX
TeX uses 72.27 points = 1 inch, as a convenient value, insignificantly
different from the American Typefounders Association.
For Continental points, TeX uses 1157 didot point = 1238 point.
Interleaf
Interleaf uses 1 pica = 0.165825 inches.
Didot (1770)
Didot defined the point to be 1/72 of a French inch in 1770. The
conversions below assume 1 French inch = 27.070 mm.
Continental typefounders
Continental typefounders quote the Didot point as 0.376065 mm.
Experimental measurements of English and American type found that
typical tolerances are that 1 point = 0.1660 +/- 0.0001 inch.
Measurements were made to an accuracy of 0.000001 inch.
Anglo-American Pica (inch) Point (inch) Pts per inch
Monotype et al 0.1660000000 0.0138333333 72.2891566265
Monotype (rounded point) 0.1659960000 0.0138330000 72.2908985759
MacKellar, Smiths, Jordan 0.1660184043 0.0138348670 72.2811428571
American Typefounders Ass 0.1660440000 0.0138370000 72.2700007227
(ditto) old inch 0.1660443321 0.0138370277 72.2698561827
TeX 0.1660440017 0.0138370001 72.2700000000
Interleaf 0.1658250000 0.0138187500 72.3654454998
Continental Cicero (inch) Point (inch) Pts per inch
Monotype et al 0.1776000000 0.0148000000 67.5675675676
Rounded metric equiv 0.1776377953 0.0148031496 67.5531914894
Didot (1770) 0.1776246719 0.0148020560 67.5581824898
Continental typefounders 0.1776685039 0.0148057087 67.5415154295
TeX 0.1776685169 0.0148057097 67.5415105008
Anglo-American Pica (mm) Point (mm) Pts per mm
Monotype et al 4.2164000000 0.3513666667 2.8460297884
Monotype (rounded point) 4.2162984000 0.3513582000 2.8460983691
MacKellar, Smiths, Jordan 4.2168674699 0.3514056225 2.8457142857
American Typefounders Ass 4.2175176000 0.3514598000 2.8452756190
(ditto) old inch 4.2175260351 0.3514605029 2.8452699285
TeX 4.2175176422 0.3514598035 2.8452755906
Interleaf 4.2119550000 0.3509962500 2.8490332874
Continental Cicero (mm) Point (mm) Pts per mm
Monotype et al 4.5110400000 0.3759200000 2.6601404554
Rounded metric equiv 4.5120000000 0.3760000000 2.6595744681
Didot (1770) 4.5116666667 0.3759722222 2.6597709642
Continental typefounders 4.5127800000 0.3760650000 2.6591147807
TeX 4.5127803293 0.3760650274 2.6591145866
----------------------------cut here-------------------------------------
Many thanks
Cheers
Woody
,