You can perform calculations that manipulate variables. This powerful feature of the site and can be used in two ways - computing numbers and interpreting results (ranges of numbers). Parameters include value, memo, and show. "value" has some special formatting which can be tricky. "memo" is used to label the calculation or for some helper text. "show" is useful for hiding a calculation performed earlier in a form that you don't want to reveal until further on down in the form (this seems esoteric but it does come up occasionally).