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The example below shows how you can sum up the amount field from a using the Form Grid.
Figure 1: Configuring and Obtaining the Field ID from a Form Grid
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Figure 3: Calculation Field in Action
Using JavaScript Math Object in Equation
The "Equation" setting of Calculation Field supports Javascript Math Object. For example, to find the max number among several fields in a form, you can use Math.max() in the "Equation". 