The formulas assume coherent units: volts, amps, ohms, and watts. Prefixes are exact decimal scale factors, not labels to ignore. Converting each input to its base SI quantity before arithmetic prevents the most common thousand- and million-fold mistakes.
Read every prefix as a power of ten
Milli means 10⁻³, micro means 10⁻⁶, kilo means 10³, and mega means 10⁶. Therefore 500 mV is exactly 0.5 V, 250 µA is exactly 0.00025 A, and 4.7 kΩ is exactly 4700 Ω.
Normalize before multiplying or dividing
For 5 V across 220 Ω, calculate 5/220 A, not 5/220 mA. The exact result is 1/44 A. Only after the formula may it be displayed as approximately 22.727273 mA. This order keeps the equation dimensionally consistent.
Display units do not change the quantity
0.022727 A and 22.727 mA describe the same current. A readable result may choose a prefix near unity, but the calculation should retain one normalized value so later outputs never depend on a rounded display string.
Case and symbols carry meaning
Use m for milli and M for mega. Use Ω for ohms when available, while a text export may use ohm for portability. µ and the ASCII letter u can both describe micro in user interfaces, but the normalized factor remains exactly 10⁻⁶.