Summed value of values in current record and previous record

Question asked by jetserkok on Apr 20, 2015
Latest reply on Apr 21, 2015 by philmodjunk

Title

Summed value of values in current record and previous record

Post

Couldn't find anything on the internet on this, but perhaps i'm not using the right keywords. An example of what i want:

Record 1: value a = 10, value b = 5, value c = a - b (so value c = 5)
Record 2: value a = 3, value b = 2, value c = value c from record 1 + a - b (so value c here is 5 + 3 - 2 = 6)

The starting value of value c = 0, and then for each subsequent record it need to take into account the previous record's value. Much like in excel is done often te keep a 'saldo' of something, for example the cash machine in a shop. When in this case the starting value is zero, then on the first day (record 1) 10 euros is sold and 5 euros is spent, so after day one, there is 5 euros left. Then on the second day 3 euros is sold and 2 euros is spent, so the accumulated value is now 6.

Any help is appreciated.