In Mathematics, the operator provide on keyboard is quite clear for addition, subtraction and divide as the follow + - /
The multiplication * might be familiar as the multiplication for programmer but i do not sure about ordinary user. I don't know should i use '*' or 'x' for multiplication sign.
The purpose is to provide user detail of how each field will be used
One drawback i can think of if using x might be rely on font face and if user changing to others font x might not be appear like multiple.
Also, by the standard * (asterik) should be used to multiplication but i don't sure for its readily.