Your formulas can use conditional if - else statements using the c++ style ternary operator:
condition ? expression_if_true : expression_if_false
For ex: Say you have a measurement or variable called #num_of_darts, for it’s formula you could use something like:
@waist_circ >= 30 ? 2 : 1
where if the waist measurement >= 30 (in) the number of darts = 2. If the waist measurement is less than 30in then the number of darts = 1.
You can also nest conditionals inside as another expression:
@waist_circ >= 30 ? 2 : ( @waist_circ >=24 ? 1 : 0 )
where now if the waist is < 24 number of darts = 0. If the waist >= 24 AND < 30 then the number of darts = 1. If the waist >=30 then the number of darts = 2.
Other uses may be adapting pocket size to the size of jacket, allowing extra SA for larger sizes.
For more reading on the subject: