How do I make a form field validate that it is the sum of two other fields?

Question

Hi there,
I am creating a form, and I would like one of the fields to validate by making sure that this field is the sum of two other fields in the form.  Does anyone have any ideas on how to go about this?  I know I'll need to run a custom validation script, but I'm not sure where to begin - I've never done one for validation before.
Thanks for any help!

Answer 1

OK, here's a sample script that I hope will clearly demonstrate the general approach. It is intended to be the custom Validate script of the field that the user enters that value that is supposed to be equal to the sum of the two others.
// Custom Validate script
(function () {
    // Get the value that the user entered
    var sVal = event.value;
    // If it is blank, do nothing else
    if (!sVal) {
        return;
    // Convert string to a number
    nVal = +sVal;
    // Get the values of the fields, as numbers
    var v1 = +getField("text1").value;
    var v2 = +getField("text2").value;
    // Add them together, rounding to two decimal places, converting to number
    var sum = +util.printf("%.2f", v1 + v2);
    // Compare entered value to the sum of the other two fields
    // Alter the user if they do not match
    if (nVal !== sum) {
        app.alert("The value you entered does not equal the sum of text1 and text2. Please correct.", 3);
        // If you want the entered value rejected, include the following
        event.rc = false;
Replace "text1" and "text2" with the actual field names.