Black-out

Last week, Barbara Flores and I did a training session about metrics. During our studies for this presentation, we found some interesting information about black-out (the period of time in the beginning of the project in which no information is available).

According to Alistair Cockburn, this amount of period is defined by the unit of measure chosen to be used in the Y axis. The coarser is the unit, the longer is the blackout period.

Here we have an example extracted from Chapter 3 of “Crystal Clear: A Human-Powered Methodology for Small Teams” (Alistair Cockburn, Addison-Wesley, 2004).

This charts are based in the "house packing" example. The chart in the left shows in Y axis the number of floors. The chart in the right shows the number of rooms (a much smaller unit of measure).

We can notice that using floors as a measure unit we would take almost 15 days to discover that packing would take much more time than expected. Using rooms as a measure unit, you would take only 3 days to discover it.

So, keep one thing in mind: choose the smaller non-expandable unit of measure, because the smaller the unit is, the shorter the initial black-out period will be.