One of the fastest ways of debugging your expressions and variables is by using an INPUT BOX. The input box can show several variables at once and any type of QlikView expression can be written and evaluated directly in an input box.
Create a new input box and add your three variables like this:
Then you can immediately inspect all three variables and modify them to see what it evaluates to.
Example - if you have the two variables Var_1 and Var_2 populated with 456 and 890:
It might seem like your variables don't evaluate to numbers - thus adding them together will not give you a numeric result - possibly and error. Like this:
For me Input Box is an invaluable aid in getting my expressions correct and saving a lot of time while debugging them.