Entity Formula Subtraction - Not working - even on Demo site. Bug?

[khopper]

Entity Formula Subtraction - Not working - even on Demo site. Bug?

// Enter '0' if vaule NULL
ifThen(profit == null,profit == '0');
ifThen(financeamt == null,financeamt == '0');
ifThen(phonesystemcommission == null,phonesystemcommission == '0');

// Calulate Profit
ifThenElse(profit == '0', profit == (financeamt - phonesystemcommission),'20000');

[item]

Hello,
typo error i think : assignment is "=" => one =
double = (==) is for comparaison.