Define your variables

Here you define the variables that you want to use in your calculation.
pat_weight = 80; pat_height = 1.80;
Please note, if you are using dates, you need to add quotation marks, e.g.:
inc_date = "20-05-2016";

Calculation template

Here you write your calculation field template just as you would in Castor.
{pat_weight}/({pat_height}*{pat_height});

Syntax check

If there are any issues with your script, they will appear here.

Final formula

This is what your final formula will look like.

Result

This is the output of the calculation.