Read the bands on a carbon-composition or film resistor, or type a value and watch the bands appear. Works both ways, in four-band and five-band, with the tolerance ring included.
Two significant figures on a four-band resistor, three on a five-band. The multiplier band sets the decimal place; the last ring is tolerance.
| Color | Digit | Multiplier | Tolerance |
|---|---|---|---|
| Black | 0 | × 1 | — |
| Brown | 1 | × 10 | ±1% |
| Red | 2 | × 100 | ±2% |
| Orange | 3 | × 1 k | — |
| Yellow | 4 | × 10 k | — |
| Green | 5 | × 100 k | ±0.5% |
| Blue | 6 | × 1 M | ±0.25% |
| Violet | 7 | × 10 M | ±0.1% |
| Grey | 8 | × 100 M | ±0.05% |
| White | 9 | × 1 G | — |
| Gold | — | × 0.1 | ±5% |
| Silver | — | × 0.01 | ±10% |
| No band | — | — | ±20% |
Most resistors in a tweed- or plexi-era amplifier are carbon composition — a slug of carbon and binder molded around the leads. They are cheap, quiet enough for audio, and shrug off the brief overloads a guitar amp hands them. What they are not is precise. A gold tolerance ring means ±5%, silver means ±10%, and a resistor wearing no fourth band at all was sold at ±20%. A "100 k" plate resistor from 1959 could have left the factory anywhere from 80 k to 120 k and still been in spec.
Age widens the gap. Carbon composition drifts — almost always upward — as the binder absorbs moisture and decades of heat cook the slug. It is routine to pull a half-century-old resistor and measure it 10–20% high, sometimes more where it ran hot next to a power tube. That drift is why a vintage amp rarely matches its printed voltage chart node-for-node, and why builders chasing an original tone often measure the old parts before deciding which to keep. The reference library lists the datasheets and era-component sources behind those original values. That is a component's own ±20% tolerance — a different, unrelated ±20% is the reading tolerance Fender printed on its own voltage charts, covered in the units & notation guide.