Operators are symbols indicating how to combine two values or subexpressions. They include the standard arithmetic operators (+ [addition], - [subtraction], * [multiplication], / [division]); comparison operators (=, <>, <, >, etc...); logical (or Boolean) operators (And, Or, Not); and the parenthesis symbols for indicating precedence.
Transaction.Gross * 1.5
"Tax Invoice " + Transaction.OurRef
Transaction.DueDate - 5