I would like to calculate moving summary‏‏‏‏‏:

```

Total amount:100
first receipt: 20
second receipt: 10

```

the first row in calculation column is a difference between total amount and the first receipt: 100-20=80

the second row in calculation column is a difference between the first calculated\_row and the first receip: 80-10=70

The presentation is supposed to present receipt\_amount, balance:

```

receipt_amount | balance
20 | 80
10 | 70

```

I'll be glad to use your help
Thanks :-)