As pressure on a gas decreases, the gas expands and cools; increasing pressure makes the temperature rise. You could also express these phase changes as evaporation and condensation, which is how evaporator coils and condenser coils get their names. Refrigerants, including Freon and Puron, may never need recharging throughout the life of your AC.
1 Make sure that the start of the ruler is directly below the center of one eyeâs pupil. 2  Hold the ruler (keeping it steady and parallel to the floor); mark the location on the ruler of the other eyeâs pupil. 3  Measure the distance in millimeters between the two marks. 4  That distance will be your PD.
Ask Your Doctor. You can also get this information from your doctor or from a licensed optician. If you have two PD numbers on your prescription, you have either been given both the Distance/Reading or Right Eye/Left Eye. Here's what you do: Two same number: (Ex. 30/30) Add them together (Ex. 60 is your PD). Two low numbers*: (ex. 30/31) The first number is for the right eye (O.D.) and the second number is for the left eye (O.S.). *Place it in the Customer notes section of the order form. Two high numbers: (Ex. 62/59) First number is your Distance PD and the second is your Near PD (for reading-only glasses). As a Guideline: Most adults' PD's are between 55-65. Most kids' PD's are between 42-54.