Customer-specific construction contracts are recognised at percentage of completion. This means that the prorated sales and the costs of sales incurred are recognised at the percentage of completion, based on the contractual arrangements with the customers, reached by the balance sheet date, as soon as the results of the construction contract can be reliably estimated. Percentage of completion is calculated on the basis of the project costs incurred by the balance sheet date as a proportion of the total costs of the project. In the balance sheet, the sales posted in line with their percentage of completion are reduced by advance payments received and recognised under trade receivables. As soon as the result of a construction contract cannot be reliably estimated, the revenues from the contract are only recognised at the level of the contract costs incurred and which are probably collectible. Losses on contracts are immediately expensed in full as soon as they are expected.