here borrow the most interesting.

We know that in France the fundamental standard for measures of length
was for a long time the _Toise du Châtelet_, a kind of callipers
formed of a bar of iron which in 1668 was embedded in the outside wall
of the Châtelet, at the foot of the staircase. This bar had at its
extremities two projections with square faces, and all the _toises_ of
commerce had to fit exactly between them. Such a standard, roughly
constructed, and exposed to all the injuries of weather and time,
offered very slight guarantees either as to the permanence or the
correctness of its copies. Nothing, perhaps, can better convey an idea
of the importance of the modifications made in the methods of
experimental physics than the easy comparison between so rudimentary a
process and the actual measurements effected at the present time.

The _Toise du Châtelet_, notwithstanding its evident faults, was
employed for nearly a hundred years; in 1766 it was replaced by the
_Toise du Pérou_, so called because it had served for the measurements
of the terrestrial arc effected in Peru from 1735 to 1739 by Bouguer,
La Condamine, and Godin. At that time, according to the comparisons
made between this new _toise_ and the _Toise du Nord_, which had also
been used for the measurement of an arc of the meridian, an error of
the tenth part of a millimetre in measuring lengths of the order of a
metre was considered quite unimportant. At the end of the eighteenth
century, Delambre, in his work _Sur la Base du Système métrique
décimal_, clearly gives us to understand that magnitudes of the order
of the hundredth of a millimetre appear to him incapable of
observation, even in scientific researches of the highest precision.
At the present date the International Bureau of Weights and Measures
guarantees, in the determination of a standard of length compared with