[IAmBroom]

> For example, resistors vary widely from their marked resistance

Resistors are sometimes marked with their variance band (+/-1%, for instance) to account for this.

Engineers take these expected variances into account when designing circuits. If your design is sensitive to a 3% variance in resistor value, you'd better not be specifying gold-banded +/-5% lots.

[WalterBright]

Yes, I know. I also don't know any engineer who bothered doing it (yes, I'm sure some do in critical circuits).

Capacitors also vary, and degrade over time. Semiconductors also have variances and non-linear hard-to-model behaviors. Behaviors change with heat. Few people worry about it.

Vacuum tubes are known for their wacky behaviors, which are treasured by people who make guitar amplifiers. The Melotron is well known for being highly sensitive to humidity.

[toast0]

Resistors without a tolerance marking are speced at +/- 20%.

And they might not be temperature stable either.