\danger The units have been defined here so that precise conversion to~sp
is~efficient on a wide variety of machines. In order to achieve this,
\TeX's ``pt'' has been made slightly larger than the official printer's
point, which was defined to equal exactly $\rm.013837\,in$ by the American
Typefounders Association in~1886 [cf.~National Bureau of Standards
Circular~570 (1956)]. In fact, one classical point is exactly
$.99999999\pt$, so the ``error'' is essentially one part in $10^8$.
This is more than two orders of magnitude less than the amount by which