Calculated fields are supported with the textbox table question style.
To add a calculation right click on the textbox table and select the Edit Default Values option.
The follow options are supported by entering the syntax below into the cell to be calculated:
Summation: =sum(r2c2:r2c4) - this will sum the contents of row 2 from column 2 to column 4.
Calculations: =r2c2*r2c3/200 or = r1c1/r1c4*100% (the percent sign is optional and will add a % sign to the result)
If else logic: =(if(r2c2==0) s = 0; else if(r2c2 >= 1) s=2; else s = 3;
Note about row and column references: The tables include a column and row for table labels. These are row 1 and column 1. When referencing cells the first textbox cell is typically r2c2.