h6. [[Programmer's Reference Manuals]] h6(. » [[Events]] h6((. » [[Event Numbers]] h6(((. » [[Event 21|Expansion Event]] h6((((. » Event 21,4 h2. Mouse alternate positioning device update |_<^{width:4em}. Entry | | |<^. R0|<^. 21 (&15) | |<^. R1|<^. 4 | |<^. R2|<^. Signed X change in position of alternate device (positive = right)| |<^. R3|<^. Signed Y change in position of alternate device (positive = “up”/away from user)| h4. Use The OS issues this event when the pointer driver indicates a change in the position of the "alternate positioning device" (i.e. scroll wheel). Software which receives this event via [[EventV]] can claim the vector call in order to prevent the accumulator values returned [[OS_Pointer 2]] from being updated. Drivers should use [[PointerV 4]] or [[PointerV 9]] to communicate changes in the alternate positioning device to the OS. h4. See also * [[EventV]] * [[OS_Pointer 2]] * [[PointerV 4]] * [[PointerV 9]]