ABSTRACT
Diagonal movement of terms from one side of an equation to the other is necessary so that the value of the equation is not changed. The mathematical reason for this is similar to that described regarding diagonal movement of multiplication or division terms. Most water and wastewater treatment calculations involve only multiplication and or division of terms, with no addition or subtraction. For these basic calculations, only one rule of movement must be remembered: move terms diagonally from one side of the equation to the other. Two water and wastewater calculations that involve only addition and subtraction are perimeter problems and chlorine dosage or demand or residual problems. Some of the more complex water and wastewater calculations include addition and subtraction of terms as well as the usual multiplication and division.
