Jack Ganssle has some more thoughts on "typ" numbers.
I wrote last year about the folly about using “typical” specs when designing systems. My sense from reading the comments is that a lot of responses were from older engineers. As one of those myself, I have to confess that eons ago, as a freshly-minted EE, I was a rather careless designer. Need a pull-up? Any old resistor would do. Capacitors? Sure, select one based on voltage and capacitance. I rarely thought about tolerances, temperature effects, and the myriad other factors that make a circuit reliable in production.
But sometimes there were problems, and I learned that between the lab and the manufacturing line lies a huge gulf.
Fortunately, a mentor appeared, an older engineer who was a complete pain in the you-know-what. He critiqued everything. We had to justify the smallest design decisions. He’d demand small changes to meet his notion of getting things reliable.
We all hated him.
But a strange thing happened. These carefully-reviewed designs worked. All the time. Customers weren’t ticked off. And it turns out that it’s actually interesting and rewarding to think through design decisions with care.
Another mentor appeared, a chemical engineer turned sailing bum. He taught me to apply the engineering method to building and maintaining ocean-going sailboats, where failures can be life-threatening. No fitting was too unimportant to think about from a stress, wear, and materials standpoint. Dan taught me to generalize the engineering mindset to life in general. Some politician makes an odd claim? Do the numbers. What’s likely to happen to the teenagers on that weekend at the beach? Do a worst-case analysis and develop contingency plans.
It drives my wife crazy.
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