When replacing an capacitor, typically a motor start or motor run capacitor, an oddity may appear. A capacitor that lists two different values on the case. Such as the example below:
The immediate thought that this capacitor is both 540uf and 648uf is reasonably confusing. However, there is a value from this capacitor that is missing, the tolerance.
What this capacitor is stating is a capacitance rating of 540uf, with a tolerance of -0%/+20%.
If the higher value is not 120% the lower value, then it is likely a tolerance will be equal both positive and negative (+/- 10%).
In which case true value of the capacitor is directly in-between the listed values. Simply add the two values together and divide by 2.