Cockpitdecks manipulates values that can come from different sources:

1. Variable are simple scalar typed values (mainly string, float or integer). They can either come from the simulator software or Cockpitdecks internal values. They are scalar variables.
2. Value are complex scalar typed values that combines on one or more Variable in a Formula expression which ultimately provide a single final value.

Values are used by buttons and observables. Values are used when there is a need to combine and modify raw values as provided by the simulator or by Cockpitdecks into another meaningful value through simple mathematical operations or rounding.

Variables and values have listeners. Listeners are other objects inside Cockpitdecks that are using the variable or value. When the variable or value changes, each listener is notified of the change and can act accordingly.

For example, Values are notified when one of its underlying Variable has changed. This allows the Value to compute its new value. the Value in turn notifies the Button or the Observable that relies on it of its change. The Button or Observable can then adjust as needed.

Changes of Data value enter Cockpitdecks through Data Events. The SimulatorDataEvent (or one of its sub-class) is used to report the change of a value in the simulator software. The CockpitDataEvent (or one of its sub-class) to report change of value in the Cockpit.

Formula

A Formula is a Variable that consist of an expression using other Variables.

	formula: ${sim/cockpit2/gauges/actuators/barometer_setting_in_hg_pilot} 33.86389 * round

When one of the constituing variable of a formula changed, the formula is reevaluted.

The value of a formula can be used in a text expression as ${formula}.

There can only be one formula expression per activation and one formula expression per representation. (An Annunciator that has several annunciator parts can use a Formula in each of its individual part.)