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C00007 00003	  1) ERRTEX.LYL[MF,DEK] and 2) ERRATA.TXT[TEX,DEK]	12-08-80 14:02	pages 9,9
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**** File 1) ERRTEX.LYL[MF,DEK]/9P/4L
1)	* Page 178, a new binary relation \heqv (Hardy equivalence symbol) now lives
1)	in position '067 of the symbols fonts.
1)	* Magnified printing and \chpar12:
1)	It is frequently valuable to be able to control the magnification factor at
1)	which documents are printed.  For example, when preparing document masters
1)	that will be blown down by some factor at a later step in the printing
1)	process, it is helpful to be able to specify that they be printed blown up by
1)	that same factor.  There are several new features in TEX to allow for greater
1)	ease in the production of such magnified documents.
1)	TEX should be thought of as producing as output a "design document":  a
1)	specification of what the final result of the printing process should look
1)	like.  In the best of worlds, this "design document" would be constructed as
1)	a print file in a general and device independent format.  Printing a
1)	magnified copy of this document for later reduction should be viewed as the
1)	task of the printer and its controlling software, and not something that TEX
1)	should worry about.  But real world constraints force us to deviate from this
1)	model somewhat.
1)	First, consider the plight of a TEX user who plans to print a document
1)	magnified by a factor of two on a printer that only handles 8.5" by 11"
1)	paper.  In order to determine an appropriate \hsize and \vsize, this user
1)	will have to divide the paper dimensions by the planned magnification factor.
1)	Since computers are so good at dividing, TEX offers this user the option of
1)	setting the "magnification" parameter to 2000, warning TEX of the anticipated
1)	factor of 2 blow up, and then specifying \hsize and \vsize in units of
1)	"truein" instead of "in".  When inputting a "true" distance, TEX divides by
1)	the scale factor that "magnification" implies, so as to cancel the effect of
1)	the anticipated scaling.  Normal units refer to distances in the "design
1)	document", while "true" units refer to distances in the magnified printer
1)	output.
1)	Secondly, some existing print file format and printer combinations have no
1)	current provision for magnified printing.  A Press file, for example, uses
1)	absolute distances internally in all positioning commands, and Press printers
1)	treat these distances as concrete instructions without any provision for
1)	scaling.  There is a program that takes a Press file and a scale factor as
1)	input and produces as output a new Press file in which all distances have
1)	been appropriately scaled.  But it is inconvenient to be forced to use this
1)	scaling program on a regular basis.  Instead, the Press output module of TEX
1)	chooses to scale up all distances by the "magnification" factor when writing
  1) ERRTEX.LYL[MF,DEK] and 2) ERRATA.TXT[TEX,DEK]	12-08-80 14:02	pages 9,9

1)	the output Press file.  Thus, the Press files that TEX writes are not
1)	representations of TEX's abstract "design document", but rather
1)	representations of the result of magnifying it by the factor (\parval12)/1000.
1)	Caveat:  Due to the manner in which the current implementation of TEX writes
1)	Press files, it is not permissible to change the value of parameter 12 in the
1)	middle of a TEX run.  If you want to produce magnified output, you should
1)	reset parameter 12 once very early in your document by using the  \chpar12
1)	control sequence, and from then on leave it alone.  In particular, because of
1)	the implications of the feature discussed in the following section, the value
1)	of parameter 12 must not change after the first font in your document has
1)	been specified (by a \font control sequence).  This restriction means that
1)	you cannot begin your document by inputting the standard "basic.tex" file if
1)	you want to use a magnification different than the one it specifies.
1)	* Magnified fonts, an extension to \font:
1)	The magnification mechanism has been extended to include font specifications
1)	as well:  in order to print a document that is photographically magnified, it
1)	is essential to use magnified fonts.  A font is specified by the "\font"
1)	control sequence, which now has the syntax
1)		"\font <fontcode>=<filename> at <dimen>".
1)	The "at" clause is optional.  If present, the dimension specified is taken
1)	as the desired size of the font, with the assumption that the font should be
1)	photographically expanded or shrunk as necessary to scale it to that size.
1)	For example, the two fonts requested by the control sequences 
1)		"\font a=CMR10 at 5pt" and "\font b=CMR5 at 5pt"
1)	will look somewhat different.  Font a will be CMR10 photographically reduced
1)	by a factor of two, while font b will be CMR5 at its normal size.
1)	The dimension in a font specification can use any units, either standard or
1)	"true".  The interpretation of "true" here is identical to its interpretation
1)	in the specification of any other distance:  asking for a font "at 5pt"
1)	requests that the font be 5 points in size in TEX's "design document", while
1)	asking for a font "at 5truept" requests that the font be 5 points in size
1)	after the scaling implied by the "magnification" factor.
1)	If the "at <dimen>" clause is omitted, TEX defaults the requested size to the
1)	design size of the font, interpreted as a design (non-"true") distance. 
1)	Thus, the control sequence "\font a=CMR10" is equivalent to the sequence
1)	"\font a=CMR10 at 10pt".  
1)	Caveat:  This extension allows the TEX user to request any magnification of
1)	any font.  In general, only certain standard magnifications of fonts will be
1)	available at most printers.  The user of TEX at any particular site must be
1)	careful to request only those fonts that the printer can handle. 
1)	* Page 40,  there are two new units of distance:
1)		bp	"big point"  (one inch equals 72 "big points")
1)		mi	mica  (one millimeter equals 100 micas)
**** File 2) ERRATA.TXT[TEX,DEK]/9P/4L
2)	Page 178, a new binary relation \heqv (Hardy equivalence symbol) now lives
2)	in position '067 of the symbols fonts.
***************