Formulas - Programming Difference

[blumarble]

Here's an example I'd like to create. It's pretty simple, but I've also found the help files less than helpful; too much unexplained.
I've got a schedule that lists room areas. I'd like to add two parameters: one where I can enter the programmed area for each room and another that calculates the difference between the two. (actual area - programmed area = difference +/-). I can export it all to a spreadsheet, but I'd like to see the changes in "real time". Thanks.

[blumarble]

Here's some additional info. In the first attached jpg, what type(s) should my new parameters be? Area? Number? One will be an entered value (programmed SF) the other will be a calculated value (current area - programmed area).
In the second attached jpg, what is the "name"? Is this a variable to be used in the formula? If I enter a used parameter, it says it's already in use. Again, what "type" should I use? Finally, what would the formula be? Everything I've tried to enter so far (e.g. "programSF - SFdifference") tells me I've got a "type mismatch".

[aaronrumple]

Here's some additional info. In the first attached jpg, what type(s) should my new parameters be? Area? Number? One will be an entered value (programmed SF) the other will be a calculated value (current area - programmed area).
In the second attached jpg, what is the "name"? Is this a variable to be used in the formula? If I enter a used parameter, it says it's already in use. Again, what "type" should I use? Finally, what would the formula be? Everything I've tried to enter so far (e.g. "programSF - SFdifference") tells me I've got a "type mismatch".
The type should be area. Once set, it can't be changed. You would have to delete the old one and recreate.

[blumarble]

(see attached) Both the new parameters are defined as "area". Now what?

[aaronrumple]

(see attached) Both the new parameters are defined as "area". Now what?
Youve got too much stuff going on.

All you need is:
programSF - Area
This generates a value for diffcalc. differenceSF is extraneous.

No equal sign. No this equals that required.