From the Ask Tom mailbox:

Question:
You said that Time Span could be used to measure complexity. Not sure I understand the connection?

Response:
There are two kinds of complexity in the world. Time Span can be used to measure one of them.

The first kind of complexity is detail, detailed complexity. This is the world of engineering. Computers are useful in managing detailed complexity. Lots of moving parts.

But there is another kind of complexity, more difficult to deal with. It is the uncertainty in the future. And the further something is, out in the future, the more uncertain it is.

If you have a project that must be completed by tomorrow, the level of uncertainty is small. You will only be using materials on hand, working with people you already know, with guidelines that are already nailed down, because the project must be completed by tomorrow.

If you have a project that will take 24 months to complete, all kinds of things can change between now and the project due date. The material you intended to use may no longer be available when you need it. The people you work with now may be different than the people you work with next year. And the guidelines you have in your hand now, will most definitely change between now and 24 months from now.

The complexity of a one day task assignment versus a 24 month task assignment can be calibrated by simply measuring the Time Span of the due date.