Axis coordinates may be returned as relative values; that is, the amount by which they have changed since the last call to the IDirectInputDevice::GetDeviceState method or, in the case of buffered input, since the last item was put in the buffer.
Absolute axis coordinates are a running total of all the relative coordinates returned by the system since the device was acquired; in other words, they show the position of the axis in relation to a fixed point.
By default, mouse axes are reported as relative coordinates and joystick axes as absolute coordinates. You can use the IDirectInputDevice::SetProperty method to change the default behavior of any axis or all the axes of a device.