About Capacitance Value
There are many different types of capacitors in the market like the mica, ceramic, electrolytic, tantalum and etc. Different types of capacitor have difference tolerance value. In order to avoid the confusion of what is the tolerance value of each type of capacitor, i would just use minus 10% as a guideline. For example, if the non polarity capacitor have the value of 1 nano farad (nf) then this mean when we test the capacitor, the value should not go below 0.9 nf otherwise we have to replace the cap. Even if the cap is in the borderline (say 0.9 or 0.91nf) , i would still replace it because i believe the cap value will continues to drop after few months time.
For electrolytic capacitor, we can use the ESR meter thus not necessary to know about the capacitance value although there are some rare cases where the ESR check to be okay but the capacitance value were out.