Why does my capacitor list two values?

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.

The motor start capacitors do not need to be as exact as motor run caps so they are marked with two values meaning the the capacitance is somewhere in between the two values and that is another reason there is no tolerance rating just a range.