David Kastrup wrote:
No, it isn't. It is a matter of multiplication, division and truncation.
It is a little-know fact that 2.54cm are 72.2698pt in TeX, 1in is 72.26999pt, and both are different from 72.27pt, while 254cm and 100in perfectly well are 7227.0pt.
So no, you can't substitute a unit in TeX with a constant. Units are _fractions_ of sp, and applying a "multiplier" to them does not work like one would think.
Valid points. I don't see much use in a generic converter, but tex.sp "string" is a quick and simple extension. Although I do fear that dimen_to_number (in ltexlib.c) will need un-fixing to be totally compatible with TeX82: I am using strtod() and the documented conversion ratios there instead of the actual code from Knuth. Best wishes, Taco