In article t,
Ralph Mowery wrote:

Capacitors such as .047 have been around a long time. I don't know why
it is such an odd value as I doubt the extra .003 would be noticable in
the circuits most of them are used in. As the tollorance on most of the
electrolytics are very broad I don't understand the odd values either.

If you look at the standard values used for resistors and capacitors
and inductors, you can see that they tend to be spaced in a way which
creates something approximating a geometric ratio - that is, each
value in the series is 1-point-something times the previous value.
The higher-precision value "kit" has a total of 24 values over each
decade. The common lower-precision value kit has six values (every
fourth, from the 24-value higher-precision range).

The relationships aren't exact - 0.047 would be 0.046415... and
some of the other "traditional" values are even further off of the
geometric curve. But, that's the basics of it.

I imagine that when picking the values which would go in the
lower-precision set, it was easier to just choose the same nominal
values as were used in the higher-precision set, and specify a lower
tolerance (e.g. +/- 10% for a cheap film cap, or +100/-20 for a
'lytic).