When I buy resistors and capacitors for restoring antique radios, and general electronics, I have noticed that many of the values available have values based on multiples of 2.2, 3.3 and 4.7. There seems to be no intuitively logical reason for this. Resistor values are also available in multiples of 10 and 5, and when I design a circuit, I tend to choose values that make the math easier - ie, multiples of 5 and 10.
I admit that I am probably missing something obvious here. Please help fight my ignorance…
E series - basically the rationale is that with an approximately geometric sequence you minimize the maximum factors between two values given a certain number of values per decade.
Let me elaborate on that answer. When I was invoved with electronics, over fifty years ago, the standard for cheap resistors was that the nomina value was accurate only to within 20%. So the values were chosen so that you could get to within 10% of any value. If you wanted a resistance between, say, 45 and 50 ohms, you chose a 47 ohm resistor. There were 10% resistors that cost more and came in twice as many values, as well, IIRC, as 5% resistors. If you needed more precision than that, you were in special order territory.