Expanding table: Calculating difference to value from previous row

Hi there,

I am a complete newbie to LiveCycle Designer (ES2) and have created below document with an expanding table.

Shared Files - Acrobat.com

My aim is to make the form user friendly by adding a calculation in the field "Twist" which calculates the difference from the current row to the previous row.

I have no idea about Java Script, I am afraid, and also don't know if this is possible at all so it's probably a bad idea after all.

The reason for setting it up as an expanding table is so that the form can be used for all 32 instances the form would be used for (they would all require different amount of rows altogether).

The calculation would start in row 2 (Checklist.Table1), take the twist value entered in row 2 and calculate the difference to the twist value entered in row 1.

Then in row 3, it would calculate the difference between twist value in row 3 to row 2 etc.

So subtract value of field in rowⁿ with value in row^n-1 or something in this direction.

Is there anyone at all who could help me with this at all?

I'd be very grateful for any advice you could give me.

Thanks a lot!

Mathilda