ResistorBuilder is a graphical Wolfram Language application that finds efficient ways to approximately construct a resistor with a given value by combining standard E6 series resistors in series and parallel. It turns out that within a decade (e.g., 100Ω to 1kΩ), it is possible to construct any resistance value (within ±0.3% tolerance) using only four E6 series resistors.

ResistorBuilder is fully self-contained within a single file and has no external dependencies (other than a recent version of Mathematica). Just download and evaluate ResistorBuilder.wl, and ResistorBuilder should appear as a Manipulate window at the bottom of the package window.

• Move the slider or enter a number in the text input field (between 100 and 1000) to change the target resistance.
• All resistor circuits having a combined value within ±0.3% of the target resistance are displayed underneath.
• Exact resistance values are displayed to the right of the corresponding circuits. Sometimes, there will be a circuit that exactly matches the target resistance; other times, they might all be approximate.