Some functions, for example, NOW or TODAY and the IMPORT.* functions, are Volatile Functions. This is because these functions can return a different value if they are evaluated a second time, even if all parameters passed to them have not changed.
Any formula that uses a volatile function is marked as a volatile formula and is treated differently by the IndustraForm formula engine. Non-volatile formulae are re-evaluated whenever the value is needed. The result of a volatile formula, on the other hand, is stored. It is only re-evaluated when a cell that it depends on changes value, or the Refresh Data button is pressed on the form section.