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By specifying within the formula that the sum equals 100, you are essentially turning this formula field into a binary expression. When the expression is true (X + Y + Z = 100), then the formula returns a value of 1. When the expression is false (X + Y + Z ≠ 100), the formula returns a value of 0. You can format this field to use white text so it is not visible to the signer.
Note: If you want to display the added total to the signer as they enter new values, use a different formula field that has just [X] + [Y] + [Z]. This display formula should not be used in the following logic.
Next, you must turn this the formula field into a trigger and create conditions that make it impossible for the signer to complete the form until the expression is made true (X + Y + Z = 100). To do so, you need to create two new required text fields, assign them the exact same data label, give them conflicting validations, and make them conditional to the formula field.
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