For a blend, the saturation temperatures at which the last liquid boils (dew) and the first vapour forms (bubble).
At a given pressure, a zeotropic blend starts to boil at its bubble point (the first bubble of vapour appears) and finishes at its dew point (the last drop of liquid is gone). The difference between them is the glide.
The working rule: calculate superheat from the dew point and subcooling from the bubble point. Using the wrong column on a high-glide blend throws the reading off by several degrees.
Exam work areas
B · Tools, piping and refrigerant handling E · Commissioning and start-up