[dmurray]

If you can measure them with that precision, would it make sense to sell them with that accuracy too? So if you tried to manufacture a resistor at 68kΩ +/- 20%, and it actually ended up at 66kΩ +/- 1%, couldn't you now sell it as an E192 product which according to TFA are more expensive?

Selling with different tolerances only makes sense to me if the product can't be reliably measured to have a tighter tolerance, perhaps if the low- quality ones are expected to vary over their life or if it's too expensive to test each one individually and you have to rely on sampling the manufacturing process to guess what the tolerances in each batch should be.

[retrac]

Resistors with worse tolerances may be made out of cheaper, less refined wire, which will vary resistance more by temperature. The tolerance and resistance is good over a temperature range. For more reading looking up "constantan".

[RetroTechie]

Most resistors don't use wire, but some film of carbon (cheaper, usually the E12 / 5% tolerance parts) or metal (E24, or 1% and tighter tolerances) onto a non-conducting body. Wires mean winding into a coil, which means increased inductance.

I suspect in most cases the tolerances are a direct result from the fabrication process. That is: process X, within such & such parameters, produces parts with Y tolerance. But there could be some trimming involved (like a laser burning off material until component has correct value). Or the parts are measured & then binned / marked accordingly.

Actual wire is used for power resistors, like rated for 5W+ dissipation. Inductance rarely matters for their applications.

[Gibbon1]

Accuracy depends on the technology used. Carbon comp tends have less accuracy then carbon film. And it's not true that higher accuracy is always better.

Some accurate resisters are essentially wound coils and have high inductance and will also induce and pick up magnetic interference. Stuff like that matters often a lot.

[projektfu]

Thanks, always good to remember that the tolerance of a resistor is not just a manufacturing number but also defined over the specified temperature range.

[dylan604]

Depends on where in the production line they are being tested. If they are tested after they've had their color bands applied, then you wouldn't be able to sell it as a 66kH since the markings would for a 68kH

[wongarsu]

The issue is probably volume. Very few applications need a resistor that's exactly 66kΩ, but a lot of applications need resistors that are in the ballpark of 68kΩ (but nobody would really notice if some 56kΩ resistors slipped in there).

For every finely tuned resonance circuit there are a thousand status LEDs where nobody cares if one product ships with a brighter or dimmer LED.