Yes, the supply on hand and the supply arriving from the previous row need added together. The usage rate, which is a constant is then subtracted from that. The result is the on hand total for the next day.
For example:
| Date | On Hand | Arriving | Usage Rate |
| 9/9/2014 | 100,000 | 250,000 | 100,000 |
| 9/10/2014 | 250,000 | 1,000,000 | 100,000 |
| 9/11/2014 | 1,150,000 | 0 | 100,000 |