In the 20th century, manufacturers adopted unified standards for component values. The resistance E - series, released by the IEC in 1952, uses geometric progressions for exponential spacing.

For E6, E12, E24, E48, E96, E192 series, resistance ratios are ⁶√10, ¹²√10, ²⁴√10, ⁴⁸√10, ⁹⁶√10, ¹⁹²√10 with accuracies of ±20%, ±10%, ±5%, ±2%, ±1%, ±0.5%.