One Law, Four Related Formulas
Ohm's Law — V = I x R — relates voltage, current, and resistance, but real circuit analysis constantly needs to solve for whichever of these three is unknown given the other two, plus a fourth quantity, power (P = V x I), which combines with Ohm's Law to produce several additional derived formulas (P = I²R, P = V²/R). Memorizing just V = IR isn't quite enough for practical work — being able to rearrange it, and combine it with the power formula, for whichever two values you actually have on hand is the more useful skill.
This matters immediately in practice: sizing a resistor for a target current needs R = V/I; checking whether a resistor's power rating is adequate needs P = I²R; verifying a power supply's current draw from its rated wattage needs I = P/V. Each of these is "just Ohm's Law" algebraically, but recognizing which rearrangement applies to a given problem is where a lot of early confusion actually comes from.
A calculator that shows the actual formula used for a given pair of known values reinforces this rearrangement skill far better than just producing a number, which is exactly why seeing the underlying equation alongside the result matters for genuinely learning the relationships rather than just getting an answer.