Wednesday, November 13, 2019

Micrometers, chalk, and axes


On a recent aircraft restoration project I learned this 3-step process of mechanics (who knew? You can't make this stuff up!), which in three short statements illustrates the axiom that a process, viewed end-to-end, is not better than it's worst component, and also ...

Precision and accuracy, no matter how diligent, are wasted on the poorest resolution of the process
  1. Measure with a micrometer
  2. Mark it with chalk (in our case, Sharpie marking pens), and
  3. Cut it with an axe! (in our case, shears of one kind or another, or (gasp!) the band saw)
The high precision guess
Ooops! This very process shows up in project management. See: accuracy vs resolution and the spreadsheet -- estimates that are just a bit better than a guess (the axe) are entered into cells with zillions of digits of resolution (the micrometer). Nonsense.

Domain distortion
And, we see it as domain distortion when the defined process crowd with six sigma control limits wants to port their ideas into the domain of the one sigma program office. Again, nonsense (except for the problems defining process in six sigma that is quite portable and worthy)

Small stuff gets washed out in the big picture
It seems I'm constantly explaining why/how the precision of a estimate in a work package more or less washes out at the PMO level in a Monte Carlo simulation of all the work package effects.

Monte Carlo is the 3-step process micrometer-chalk-axe writ large:
  1. Agonize over every work package estimate (micrometer, but the WP manager does this step)
  2. Enter all the WP data into a simulation package using 3-point estimates and benchmarks (chalk, likely applied by the project analyst)
  3. Run the simulation to get the "big picture" (axe)
What I find is those in the PMO wielding the axe seem to get inordinately excited about an outlier estimate here or there. If you're the axe-person, don't sweat the micrometers!


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