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From: ISW@cup.portal.com (Isaac S Wingfield)
Newsgroups: sci.electronics
Subject: Re: How were component values selected?
Message-ID: <42527@cup.portal.com>
Date: 20 May 91 15:41:36 GMT
References: <1991May19.020604.13608@deeptht.santa-cruz.ca.us>
Distribution: na
Organization: The Portal System (TM)
Lines: 27

spcecdt@deeptht.santa-cruz.ca.us (John DuBois) writes:

>I've been trying to figure out how the lists of valid component values
>for parts of various tolerance were generated.  It seems to me that the
>process for coming up with a list of, for example, 5% tolerance parts would
>be this:

...(his technique for making a list of values differing by 5%)

>I tried that, and it doesn't work. Some values are too high and some too
>low, so it isn't a matter of having a slightly incorrect multiplier, or
>truncating vs. rounding.

.... (more omitted)

>So, does anyone know how the standard list came to be?

I believe the problem is not that the *values* are too high or low, but that 
you assume that 5% *means 5%*. If I remember correctly something I read
years ago,  gold band  really means up to *six percent*, while  silver band  
is over twelve percent. We describe the tolerances as  5%  and  10%  for 
convenience. The requirement is that the tolerance bands must be contiguous,
with no gaps in between. Every resistor that is manufactured must be saleable, 
regardless of it s resistance.

Isaac
isw@cup.portal.com