Column Running Total and Subtract

I have the following table structure:

P. No. Name HID Type Amount Balance Leave
2029 ALAC AO-352 Earning 50
2029 ALAC AO-354 Ded 10
2029 ALAC AO-254 REC 5

This table contains so many records i think they are about 5000. I have grouped it on "PNo" and then on "Type", the type group contain three headings Ear, Ded and Rec. I want to create a filed that may contain following calculation:

Ear - (ded+rec), then i want to show this field in group footer.

It is possible that I can do this type of calculation on running single column.

Here's what I would do...

I would create 2 formulas. Formula1 = if type = "rec" then the value else 0
formula 2 = if type = ded then the value else 0

make them invisible

add a subtotal of each for the group, also invisble

create a formula = subtotal@rec - sub@ded
show that value.

I hope that makes sense to you.