To manufacture resistors (or other components like capacitors) of every possible value would be impractical, instead they are made in a range of ‘Common Values’. The standard was created by Electronic Industries Association (EIA) and is often referred to as the “E” series. This series is broken into different tolerances:
E3 – 50% tolerance (no longer used)
E6 – 20% tolerance
E12 – 10% tolerance
E24 – 5% tolerance
E48 – 2% tolerance
E96 – 1% tolerance
E192 – 0.5, 0.25, 0.1% and higher...