In article , "Frank
Dresser" writes:

Just as speculation, let's say cap manufacturers have learned to make
electrolytic capacitors with good precision at little extra cost. And let's
imagine that setting the target capacitance to 5% - 10% low reduces the cost
of the "active ingredients" by 5% -10%. Well, that would be a nice reward
for knowing how to do the job!

This makes very good sense.
I suspect that back in the old days, manufacturers would throw in up to 100%
extra foil plates area just to make sure they at least met the rated
capacitance. So you would get caps well over the ratings.

But yes, once they got the process down really tight, why toss in extra
material. In fact, shaving it on the low side is just what the front-office
bean coutners probably tell them to do nowadays! --Mike K.

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