Temperature compensation
WARNING: This page is about a different car, the 2001 Saab 9-3. However, it is still accessible from the selected car via links, so may be relevant.
At a certain engine load (mg air/combustion), a certain air mass is drawn into the cylinder during the induction stroke. If the engine coolant temperature or intake air temperature is low, the air will have a higher density than normal. This means that the pressure in the combustion chamber will be lower when combustion starts. At lower gas pressures, the combustion velocity is lower, which means that the ignition must be advanced.
There are two tables in the control module memory in which the number of degrees the ignition is advanced is specified depending on the coolant temperature or intake air temperature.