Software by Brian Taylor:

Resistors are normally supplied in ranges that have 6, 12, 24, 48, 96 or 192 values per decade. RVal helps you select the best values to produce a given ratio or difference, to connect in series or parallel to produce an exact value, the nearest preferred value to any given value, find the preferred value required in parallel with an existing resistance to produce a desired value or display a list of the values in one decade of any range.