The F4 key can also be used to quickly select the Base Ignition Table. The 32 by 32 base timing table indicates the location in degrees the ignition is to fire the spark plug before reaching TDC for each cylinder event. The base timing map can define any degree between 0 and 127.5 in one-half degree increments. The x-axis of the map denotes current engine speed while the y-axis denotes load in either manifold pressure when operating in standard speed density mode or in calculated manifold pressure when operating in alpha-n mode. Interpolation is automatically performed across both axes to determine the actual base timing value.