# VASSAL Reference Manual

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## Calculated Property

A Calculated Property defines a Property that has a value that is calculated by a formula each time it is needed.
Property Name: The name of the property that is used to access the formula value.
Expression: A BeanShell Expression that defines the formula that calculates the property value. Immediately to the right of the expression field, a green tick or a red cross appears as you are typing that tells you if your BeanShell Expression is valid or not. Select Use the Select button to access the Expression Builder to add expression components such as property names, operators and functions.