"How long is it, really?" [History of Physical Standards]

The story of length is a good example of the general progress of science: New experiments verify existing theories, or else they call forth new ones. In the world of standards, progress toward the twin goals of ever-smaller uncertainty and ever-wider application may occasionally falter, but over time, it will move forward. People, in general, don't like the concepts of uncertainty or error, especially in science, but that's where we technical folks live.