\chapter{Measures Made of People}

Every old unit is a piece of somebody's body or somebody's working day. The
foot is a foot. The cubit is the forearm. The fathom is the span of two open
arms, which is exactly as far as a sailor can pull in one motion of rope. An
acre started out as the land a team of oxen could plow between sunrise and
sunset, so it was smaller on heavy clay and larger on light soil, and everyone
who worked the land thought that was perfectly reasonable.

\section{The body as a ruler}

A unit taken from the body has one enormous advantage: you always have it with
you. A carpenter with no ruler can still lay out a beam in feet, and a merchant
with no scale can still count an ell of cloth against an arm. For most of
recorded history, that convenience mattered more than agreement between one
town and the next.

The problem is that bodies differ. The usual answer was to average them. A
German handbook from the sixteenth century explains how to fix the length of a
rod: stop sixteen men as they leave church on a Sunday, tall ones and short
ones as they come, line up their left feet heel to toe, and call the result the
rod. It reads like a joke, and it is also a serious piece of statistics, four
hundred years before anyone used that word \cite{kula1986}.

Where averaging was not enough, communities made a physical standard and put it
somewhere public. Grain measures were cut into the stone of market halls.
Iron bars were set into church walls. Anyone who suspected a short measure
could walk over and check, which is a form of accountability that a printed
definition can never quite match.

\section{One market, one bushel}

Standards were about trade, and trade meant taxes, so rulers took an interest
early. Magna Carta, which is mostly remembered for other things, spends a
clause on measurement: there is to be one measure of wine throughout the realm,
one measure of ale, one measure of corn, and one width of cloth. That clause
was reissued, ignored, and reissued again for centuries, which tells you how
well it worked.

It kept failing because a unit was rarely just a quantity. A measure of grain
came with rules about whether the container was heaped or struck level, whether
the grain was poured from a height or set down gently, and who held the
straightedge. Each of those rules moved a few percent of the harvest from one
side of the transaction to the other. Changing the unit meant changing who ate
better that winter, and the people on the losing side understood this perfectly
well.

\section{Why the same word meant different things}

By the eighteenth century France had the same words in use nearly everywhere
and the same values almost nowhere. The pied, the aune, the setier, and the
arpent all existed in dozens of local versions, and a merchant traveling three
days by cart could pass through several of them. Historians who have tried to
count the distinct units in use before the revolution end up in the tens of
thousands.

For local business this was workable. Everyone in a market town knew the local
setier, and disputes had a local remedy. For anything larger it was a tax on
every transaction: contracts needed conversion clauses, and every conversion
was an opportunity for a quiet adjustment in someone's favor.

That is the situation the next chapter starts from. The interesting thing about
the reform that followed is not that somebody wanted uniform units. People had
wanted uniform units for five hundred years. It is that somebody found an
argument for a particular size that no town, guild, or king could claim as
their own.
