Sat, 28 Jun 2003

Model of efficiency

This week, I saw a superb example of efficiency. A roofer, working alone, and making progress at an astonishing pace.

He was putting a new roof on an office building across the street from Spokane Software Systems where I work. For the three days prior, three men had worked to remove the old roof. At about ten-thirty on this particular morning, however, there was only one worker, and he was already a third done.

I had just looked away from the computer screen for a moment to give my eyes a break when I noticed him. He was opening plastic wrapped bundles of tar shingles. Somehow, he'd pick them up, flip them over, releasing the shingles from the wrapper which he then twirled like a towel. Just at the point where (were it a towel) you'd expect him to snap an unsuspecting victim, he brought his hands together collapsing the wrap in to a tight, plastic ball and discarded it in a box.

He repeated the unwrapping process on several packages of shingles in just a few moments. Then, without a pause in the action, he began shuttling stacks of freshly unwrapped shingles down to the edge of the roof, placing stacks diagonally up the roof where the new shingles he had already laid met bare tar paper. Each time he placed as stack of shingles, he would fan each end of it like a deck of cards.

The pace was incredible. He was just short of running from the pallet load of shingles at the peak of the roof to next pre-staging point, moving up the diagonal on the roof, back-and-forth, back-and-forth.

When the pre-staging was complete, he began nailing new shingles in place with an air powered nail gun. Bam-bam-bam…bam-bam-bam…bam-bam-bam, perhaps one every two seconds. In no time, he had completed a march up the diagonal front to the peak of the roof. Then, he turned, and on his way back to the bottom edge of the roof, flipped each bundle of pre-staged shingles over, marching them toward the advancing front.

You could literally watch the line of new shingles advance across the roof.

I had only watched a few minutes, and in that time had seem him lay three or four new rows of shingles up the roof. Amazed at his efficiency, I turned back to my own work re-motivated.

About a half-hour later, I looked up again, expecting to see significant progress. I was surprised to see virtually none perhaps only one or two rows of shingles had been laid down since I had stopped watching.

I quickly spotted the problem. There were three workers on the roof, now. One was handing the original roofer shingles, but he was no where near fast enough. And instead of pre-staging them so enough were within reach at every point along the way, the helper ran to the peek and grabbed a new stack each time they ran out.

Bringing up the rear was another roofer. He was laying shingles in a second advancing line, but without assistance and without any pre-staging. So he was constantly setting his nail gun down and fetching more shingles. When the first roofer reached the peak and returned to the bottom edge of the roof for another pass, the two roofers had to deal with their tangled air lines. The beautifully efficient work that I had witnessed earlier had collapsed in to a chaotic stagger.

The addition of two people to the job slowed progress to a crawl. Seeing it reminded me of The Mythical Man-Month. Apparently the principle holds true in disciplines other than software engineering.

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