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The standards association, EIA or whatever it was called at the time, created the list of 'standard EIA values' that were to apply to components. This happened, I think, in the 1950s or thereabouts.
The idea was to have succeeding values about the same ratio so that any component would fit into a bin and only one bin, depending on the tolerance. So a 20% spacing made for a set of values that could have a 10% tolerance, and so on.
For that reason, you won't see a 51 Ohm resistor with a 10% tolerance. All 51 Ohm resistors would then be 5% tolerance or better. A 51 Ohm resistor would also fit into a 47 Ohm 10% bin.
It's not a perfect system, but it works most of the time.
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12-06-2012, 12:55 AM
Hybrid Mode
