Reliability estimates of measurements greatly enhance their value. For example, saying the resistance of a resistor is 1000 Ω ± 50 Ω tells you much more than simply stating the resistance is 1000 Ω.
The term error is basically interchangeable with uncertainty, but does not have the same meaning as mistake. Mistakes, such as errors in calculations, should be corrected before estimating the experimental error. In estimating the reliability of a single quantity (such as resistance), you should recognize three different kinds of sources of error: