Foundations — Read multimeter measurements (V, I, R)

Before you can trust a single reading, you must know exactly what every letter, unit, and squiggle means and looks like. We build them one at a time, each from the one before, starting from nothing.

1. The wire and the charge — what is actually moving

Picture a straight copper wire packed with these marbles. Nothing forces them to move yet, so they just jiggle in place. To make them drift in one direction, we need a push. That push is the first symbol.

2. Voltage — the push ( symbol $V$, unit volt )

Notice we use the same letter $\text{V}$ twice: once for the quantity (voltage, the italic $V$) and once for the unit (volt, upright $\text{V}$). Context tells them apart — a number like $1.48\text{V}$ means "the voltage is 1.48 volts."

3. Current — the flow ( symbol $I$, unit ampere )

Look at the figure: to measure the flow, the meter is inserted across a cut in the pipe, so all the water is forced through it. This is why current is measured in series — you break the loop and become part of it.

4. Resistance — the opposition ( symbol $R$, unit ohm $\Omega$ )

5. The one law that ties them together — Ohm's Law

Now that we have all three symbols ($V$, $I$, $R$), we can state the single relationship that connects them. See Ohm's Law for the full build.

We can rearrange the one law three ways:

6. The tiny letters — prefixes (the part everyone gets wrong)

A raw number like "5" is meaningless in this topic. The small letter next to the number scales it. This scaling is covered fully in Metric Prefixes and Engineering Notation.

7. AC vs DC — the shape of the push over time

8. Two more ideas the parent leans on

How these foundations feed the topic

Equipment checklist

Test yourself — cover the right side and answer before revealing.