The Air Pressure dialog allows for input of Air Pressure (code PPPP), Amount of Pressure Tendency (code ppp) and the Three Hour Characteristic of Pressure Tendency (code a).
Air Pressure

Definition: The Air Pressure is the atmospheric pressure at mean sea-level in hectopascals (millibars).

Method of Measurement: Usually measured with a precision aneroid barometer, though a mercury barometer can also be used.

Dialog Operation: Input the Air pressure into the edit box to tenths in milibars. Code PPP is the air pressure without the decimal point and by removing the leading 1 if it is 1000mb or greater.

Definition: The Amount of Pressure Tendency is the pressure tendency during the three hours preceding time of observation. It is the net pressure change.

Method of Measurement: A barograph trace or determined by reading the barometer at the beginning and the end of a three hour interval.

Dialog Operation: Input the pressure tendency into the edit box to tenths in millibars. Code ppp is the pressure tendency without the decimal point

Definition: Three Hour Characteristic of Pressure Tendency is the characteristic of pressure tendency during the three hours preceding time of observation in hectopascals. It describes how the pressure has varied.

Method of Measurement: The barograph provides the best indicator pf the pressure tendency characteristic. The shape of the trace determines which code to use.

Dialog Operation: Characteristic of pressure tendency is determined from the appropriate description. Using the mouse or the up/down arrow keys select a description in the in the list box. This determines code a.

All traces may be viewed simultaneously by clicking the 'Display All Pressure Diagrams' button. If a selection is made from Display All Pressure Diagrams dialog, click 'Use Values' to return. Code a is automatically determined from the table.