The External Referent

The issue of using an external referent has many complexities. For example, consider standard international (SI) units. Science has long recognized the value and importance of standard measures, like ohms and grams and decibels. Really, the principle of reproducibility rests squarely on this idea--I cannot reliably reproduce your experiment if I use one type of unit and you use something else that may or may not directly translate.

On the other hand, as scientists learn more about the way things work, and develop increased precision, one familiar unit of measure after another gives way to a precise standard, usually tied to a relatively abstract and often invisible (to us) phenomenon like the width of hydrogen's line in a mass spectroscope or the number of vibrations in a finely crafted tuning fork. While these careful and deliberately defined units make science work more effectively, we often find them hard to relate to in our daily life.

The time-honored units replaced by these scientific split-hairs sprang from tasks we no longer perform or from ways of looking at the world few of us still have. The furlong, approximately 220 yards, derived from the length of a furrow--it also applied to one side of an acre and to 1000 links of chain. These units have little meaning for most people today, but when the units came into use, everyone who used them could visualize their external referent.

When Robert Crease asked his readers about their favorite standard unit, he was deluged with answers. In his follow-up post, he compares some "pre-SI" units with those in use in the lab today. Surveyors used a unit called a chain, a actual piece of metal chain 22 yards long, to measure land area--a vivid and unequivocally external referent point. Farmers and land owners could easily picture a "collop", defined as the area needed to graze "one sow or two yearling heifers or six sheep or twelve goats or six geese and a gander."

In explaining the appeal of these old, familiar, approximate, good-enough measures, author Eric Cross notes that they were:

reckoned on the things a man could see about him, so that, wherever he was, he had an almanac.

Or in other words, a different kind of external referent. It would seem to suggest that the referent we choose will serve us more effectively if we and those we intend to share our results with have some method for visualizing the basis of the referent.