Hi,
Your description is a bit vague but if i understand correctly, you can use a button to make the calculation. I havent included any logic to protect against empty fields.
form1.#subform[0].btnCalculate::click - (FormCalc, client)
grandTotal = subTotal + (subTotal * (salesTaxCbo / 100))
Assuming:
salesTaxCbo - Checkbox prefilled with tax percentage
subTotal - Numeric field
grandTotal - Numeric field which gets calculated amount.
btnCalculate - The button to calculate the grand total
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