Calculation Tag Type Properties: Calc Tab
The Calc tab allows you to construct the calculation to be performed by this tag. While a choice of Constant, Expression or Tag is provided, you would normally use only Expression.
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The Calculation field enables you to specify a constant
numeric value, an expression, or reference another tag that will be the
calculation run by this tag. The Calculation field corresponds to the
selected associated checkbox. Select Expression and click on the 
button to open the expression
editor.
This optional field allows you to provide a constant value that will be used instead of input read by the communication driver. It is commonly used when testing a new Analog Input tag when application is not attached to a live data source. Tags that are using manual data are marked on screen by a flashing exclamation mark.
Provide units of measure that the input data represents. Possible values for this field include "rpm" "degrees C", "%", etc.
Use this field to flag this tag’s data in the event that you suspect the values it is reporting might not be accurate, or when this tag has initially been created and you wish to ensure that its data is marked for extra monitoring.