Tolerance

The 1st set of numbers above represents standard resistance values available in tolerances of plus or minus 10 %. This means that the resistance might be as much as 10 % more or 10 % less than the indicated amount. In the case of a 470 ohm resistor, for instance, the value can be off by as much as 47 ohms and still be within tolerance. That is a range of 423 to 517 ohms. The tolerance is computed according to specified value of resistor and not actual value. You might measure the value of a 470 ohm resistor and find it to be 427 ohms, and it would be within 10 % of the specified value; if it measures 420 ohms; it is outside the10 % range and is a reject.

The 2nd set, along with the 1st set, of numbers represents standard resistance values available in tolerances of plus or minus 5 %. A 470 ohm, 5 % resistor will have an actual value of 470 ohms plus or minus 24 ohms, or a range of 446 to 494 ohms.

Some resistors are available in tolerances better than 5 %. These precision units are employed in the circuits where a little error can create a big difference.  In most audio and radio frequency oscillators and amplifiers, 10 % or 5 % tolerance is good enough. In many cases, even a 20 % error is fine.