Pieces of evidence are always unstable . They appear and disappear by accident. They are merely probable signs of the variable for which they are designed to evoke manifestations. To measure, we must invent a practical way to connect whatever pieces of evidence we arrange to observe with a simple idea about the probabilities of their occurrences. These probabilities, in turn, must be specified as governed by the measures we want to construct.
Squirrels are good at it.
Counting steps, arms, hands and fingers was our First Method. The trouble with Counting is the obviously unequal units which are counted. We don't count them. Weighing is a constructed abstraction . We have to invent them .