How to measure my PD?

How to measure my PD (Pupillary Distance)?
PD
If your prescription is less than -/+4.00D, you need one PD, measure one PD in mm. Measure the distance from your right eye pupil center to your left eye pupil center.
PDs
If your prescription is more than -/+ 4.00D or kids you need two PD, Measure two PD in mm.
Right PD : Measure the distance from your right eye pupil center to the middle of your nose.
Left PD:  Measure the distance from your left eye pupil center to the middle of your nose.