Conditional formatting and expression box

[Red Stapler]

Hi everyone,

I have an aging schedule broken down by days. User inputs the total
and its corresponding aging by days:

total aging 60

1-30 days 20
31-60 days 20
61-90 days 20

calculated 60

As a check the calcuated field should equal the total aging field
entered by the user. I want the calculated field, which is an
expression box to be highlighted if it doesn't equal the total aging
entered earlier. How do i use conditional formatting to achieve this
since i can't set the condition, if expression box is not equal to
total AR, highlight?

thanks in advance.