Abstract: A method of commissioning an internal combustion engine controlled by an electronic engine control unit (ECU) is described. The method of commissioning includes an engine mapping function in which the engine is mapped at a combination of speeds and loads to build up a full set of engine operating parameters which are known collectively as the engine control set (ECS). The method includes defining a speed/load mapping table and generating a graphical display of a corresponding speed/load grid (20) having a plurality of cells arranged in a grid, each cell corresponding to a particular speed/load combination in the speed/load mapping table. The engine is driven as close as possible to a selected speed/load combination (24) and the value of a selected engine operating parameter is adjusted to obtain an optimum value at the selected speed/load combination. Each unmapped cell in the grid is displayed in a first visually distinct manner and each mapped cell is displayed in a second visually distinct manner.