| Types of inventories | 31 December 2016 | 31 December 2015 |
|---|---|---|
| Mobile phones | 86.4 | 129.2 |
| Laptops, tablets and modems | 36.3 | 55.3 |
| Set-top boxes and disc drives | 42.0 | 13.2 |
| Other inventories | 114.0 | 83.3 |
| Total net book value | 278.7 | 281.0 |
Other inventories comprise primarily of raw materials used in the production of set-top boxes.
| Write-downs of inventories | 2016 | 2015 |
|---|---|---|
| Opening balance | 17.0 | 21.4 |
| Increase | 10.2 | 7.0 |
| Utilisation | (9.7) | (6.5) |
| Decrease | (1.1) | (4.9) |
| Closing balance | 16.4 | 17.0 |