| 2017 | 2018 | 2019 |
| % | % | % |
| Operating revenues | 100.0 | 100.0 | 100.0 |
| Operating costs | (81.9) | (84.9) | (85.6) |
| Gross profit | 18.1 | 15.1 | 14.4 |
| Operating expenses | | | |
| Sales and marketing | (2.8) | (2.6) | (2.6) |
| General and administrative | (2.8) | (3.2) | (3.6) |
| Research and development | (9.2) | (8.6) | (8.0) |
| Expected credit losses | — | (0.3) | (0.4) |
| Subtotal | (14.8) | (14.7) | (14.6) |
| Net other operating income and expenses | 1.1 | 3.4 | 3.5 |
| Operating income | 4.4 | 3.8 | 3.3 |
| Non-operating income and expenses | 0.7 | (2.4) | (0.1) |
| Income from continuing operations before income tax | 5.1 | 1.4 | 3.2 |
| Income tax benefit (expense) | (0.6) | 0.7 | (0.1) |
| Net income | 4.5 | 2.1 | 3.1 |
| Total other comprehensive income (loss), net of tax | (3.2) | 0.6 | 1.9 |
| Total comprehensive income | 1.3 | 2.7 | 5.0 |
| Net income attributable to: | | | |
| Stockholders of the parent | 6.5 | 5.1 | 5.5 |
| Non-controlling interests | (2.0) | (3.0) | (2.4) |
| Total comprehensive income attributable to: | | | |
| Stockholders of the parent | 3.3 | 5.7 | 7.4 |
| Non-controlling interests | (2.0) | (3.0) | (2.4) |