[SI-LIST] Re: Engineering Effort vs. Time

Peter,

Well said.

I might add that those who seet themselves up as experts owe it to their
audience to make sure the rules the promolgate are valid, so new engineers
and those without the time to do the testing can trust them.  If our
industry has a problem, this is it.


> [Original Message]
> From: Peter Arnold <parnold@xxxxxxxxxxxx>
> To: <si-list@xxxxxxxxxxxxx>
> Date: 4/25/2006 1:12:45 PM
> Subject: [SI-LIST] Engineering Effort vs. Time
>
> Dear Community,
>
> Entrenched layout practices often come up for discussion on this list
> and sometimes these are exposed as lacking an engineering foundation. It
> is interesting to step back and see why there such practices abound. I
> think it boils down to efficiency.
>
> In a perfect world we would have as much time as we liked to nail down
> everything we do on boards with justification from verifiable research.
> In the real cost-driven world we cannot do that, and we have to put our
> trust in various streams of knowledge. These include, in approximate
> order of reliability:
>
> 1) Solid research performed in your own lab
> 2) Advice from colleagues and component vendors
> 3) Rules of thumb
> 4) Advice from experts-at-large, email lists etc.
> 5) Tradition (old wives' tales, folk wisdom, the 20H rule etc.)
> 6) Superstition
>
> An engineer faced with a real-world project in real time must select
> amongst these sources, trading off time vs. potential inaccuracy, and
> will inevitably find himself doing things that cannot immediately be
> justified. This is not necessarily bad engineering practice. For
> example, traditions or advice from others could be good things to bet on
> - they are most likely based on some good work someone did once.
>
> Every engineer has to develop some intuition or meta-rules-of-thumb to
> determine which level of advice is good enough to apply to a given
> decision. Trouble is, things change over time (and are a function of
> frequency :)) What was once safely treated by rule-of-thumb may now
> require simulation. The hard part is knowing when to discard those
> successful habits of a lifetime.
>
> The points I am slowly getting around to proposing are these:
>  * In real time, it's hard to justify every design decision from scratch
>  * Rules of thumb are highly time- and cost-effective if intelligently
> selected
>  * It is essential to periodically audit your rule of thumb collection
> to determine if they are still good (or were ever good!)
>
> Thanks to the members of SI-List for publicly thrashing these things out
> so I can keep my thumbs up-to-date!
>
> Regards,
> peter arnold
>
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