Why do I get an error produced due to the declared variable #monthdiff# on changing the expression?

Why do I get an error produced due to the declared variable #monthdiff# on changing the expression?

Try the following steps: 1. Change the computed measure to an expression measure. 2. Mention Measure ID instead of Measure Name, in the expression. For example, Current formula --(Gross Sales/((Opening Stock+Closing Stock Value)/#monthdiff#+1)) Expected formula --(Sales Value at PP/((Opening Stock+Closing Stock Value)/#monthdiff#+1)).