Writing prices down in order

Every agreement carries two pieces of information: a number and a time. Write them side by side and you have a record. A record follows the order of time, not the size of the number.

We read a record from left to right: oldest on the left, newest on the right. That is not a convention, it is a necessity — time runs one way only. Whenever you look at a record, the freshest information sits furthest right.

The picture of that record is called a chart. A chart adds no new information; it simply lets your eye take the same numbers in faster. Looking at a chart is reading the notebook quickly. Nothing that is absent from the record is present in the chart: everything a chart shows you comes from somebody having agreed on a number.

A record tells you what happened, not what happened in between. If it says 100 at 09:15 and 105 at 11:20, the record will not tell you whether the number climbed steadily or fell and rose again — it wrote down two moments, nothing else. Knowing that you do not know the road between two numbers is one of the most valuable habits this course can give you.