resistorstolerance
If my schematic calls for a 1% resistor, can I use a 10% resistor that measures to the correct resistance within 1% or is there some quality to tolerance beyond what it measures Ohm-wise?
For example, my schematic calls for a 1% 1000-Ohm resistor. I have a 1000-Ohm resistor with a silver band (10%). I measure the resistor using an Ohm-meter and it reads 1008 Ohms which is within 1% of 1000. Can I use the resistor and meet the designer's intent?
If you read the datasheet for a resistor carefully you'll see other terms for change with soldering, with temperature and with time, in addition to the initial tolerance. The 'Load life' indicates aging at rated power. There may also be changes with humidity, and residue left on the PCB can affect the effective value.
High voltage resistors, in particular, can show a pronounced voltage coefficient (the resistance varies with the applied voltage).
In benign conditions, usually, a resistor will remain within its tolerance, and after it is mounted, temperature coefficient tends to be the largest factor.
Typical temperature coefficients are 100ppm/°C for a 1% resistor down to maybe 0.2ppm/°C for a precision resistor. Old school carbon film parts were often much worse than 100ppm/°C.
A 100ppm/°C resistor that is 1.000K at 25°C might be 1.0075 or 992.5 ohms at 100°C. It's probably a detail you don't need to worry about but the way the tempco is specified you might think they are guaranteeing the slope of the resistance/temperature curve, but that is not true- they only guarantee it remains within a box at stated extrema. The slope can be much higher than the overall average tempco, particularly for ultra-precise parts.
At the ppm level, even flexing the PCB can cause slight changes, especially to SMT parts.
Getting back to your 5% resistor, below is an excerpt from a major manufacturer's datasheet.
The temperature coefficient varies with the value so it's not shown, but for a 1K resistor it is -350~+500ppm/°C, average over the range of -55 to 155°C (+10.5%/-7.35%). You can also see that there are plenty of things that can cause the value to change 1% or more.
Looks like a 0.1\$\Omega\$ 2% resistor, so 4 in parallel would be 0.025 ohms.
At 2.5A the power dissipation would be 0.75W, which is plausible for the appearance, but you might want to compare the exact size against similar construction resistors.
That's probably too low for your meter to measure reliably, but you can get closer by subtracting the reading you get when you short the probes from that of the resistor.
Best Answer
Resistors based on carbon tend to have quite more noise (there are a number of noise types apart from basic thermal noise). So you usually don't want them in an audio circuit even if the accuracy itself may not be much of an issue.