Figures of Merit

Stratechery is the most recent place I’ve seen someone revive Steve Job’s metaphor of computers as a bicycle of the mind. It was this excerpt, quoting a study from Scientific American, that got me thinking about systems engineering:

The best analogy I’ve ever heard is Scientific American, I think it was, did a study in the early 70s on the efficiency of locomotion, and what they did was for all different species of things in the planet, birds and cats and dogs and fish and goats and stuff, they measured how much energy does it take for a goat to get from here to there. Kilocalories per kilometer or something, I don’t know what they measured. And they ranked them, they published the list, and the Condor won. The Condor took the least amount of energy to get from here to there. Man was didn’t do so well, came in with a rather unimpressive showing about a third of the way down the list.

But fortunately someone at Scientific American was insightful enough to test a man with a bicycle, and man with a bicycle won. Twice as good as the Condor, all the way off the list. And what it showed was that man is a toolmaker, has the ability to make a tool to amplify an inherent ability that he has. And that’s exactly what we’re doing here.

First, I love the anecdote and the metaphor. Bike making skills are why it’s newsworthy when the bear eats you, and bikes are great,¹ but not so great that we don’t use cars, airplanes, and electric scooters. Enter the systems engineering concept of figures of merit (FOM).

Scientific American’s FOM was kilocalories per kilometer, and bike riders crushed it. But my commute is 18 miles (30 km), I’m not in good enough shape to ride it in reasonable time, and I’d be soaked on rainy days. I also care about energy consumption, but not enough to outweigh these other factors.

In other words, my figures of merit are average speed, comfort during the trip, and the ability to transfer the energy storage location from my blood sugar to a tank of gas — way down the list is J/km. This tweet from Horace Dediu indicates I’m not alone and is also an interesting illustration of Marchetti’s constant, which claims that on average people spend an hour a day commuting, regardless of mode:

Understanding how transportation modes compete for miles. (Or why car sharing and transit are looking over their shoulders trying to figure out whether to run or fight.) pic.twitter.com/tbD6qksRfF

— Horace Dediu (@asymco) February 26, 2018

This is all super obvious, but deconstructing the though process illustrates how identifying and weighting what’s important affects the answer. In everyday life intuition is usually enough,² but systems engineers use this type of deliberate though process when the answer is not obvious, and to document our position on what we value.