Thursday, February 20, 2014

About micrometers, chalk, and axes

I'm nearing my one year anniversary working on a volunteer project to restore this Lockheed PV-1, circa 1942, short-range bomber and reconnaissance aircraft.

Some assembly is required!

Frankly, I'm trained as an electrical engineer -- Georgia Tech, et al -- but there's not much electrical/electronic on this aircraft. So, I've had to recall 7th grade metal shop: brakes, shears, rivets, etc.

One thing I've learned from my (mechanical engineer) team leader -- also a Georgia Tech wreck as it turns out -- is the 3-step process of mechanics (who knew? You can't make this stuff up!):
  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)
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 are entered into cells with zillions of digits of resolution. Nonsense.

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)

So it is that I have to return repeatedly in my risk management courses to why/how the precision of a estimate in a work package -- or the less frequent but more troublesome estimate outlier -- 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 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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