Electronics
Ohm's law
Current and resistance against voltage.
Readings
mA
Ω
V
Drag the red line, or type into any two boxes — the third is solved. The marked box is the one being solved for.
Print at 100% scale, then check the 100 mm bar with a rule before trusting a reading.
Why this one is an instrument
Included not because it is hard but because it is the relation most often needed while both hands are busy. Sized in milliamps and ohms, which is where small-signal work actually lives, so the useful part of the scale is the part you get.
- Equation
- V = I · R
- Constants
- I in mA, R in Ω, V in V
- Ranges
- I 1–1000 mA · R 1–10000 Ω
- Reading
- Any two values fix the third. Outside the printed ranges the instrument stops being valid — that is what the end marks are for.
These are drawn from the stated equation and nothing else. Where an equation is itself an approximation — hyperfocal distance and tap drill sizes both are — the instrument inherits that approximation exactly, no better and no worse.