al_set_mouse_wheel_precision - Allegro 5 API

       Sets  the  precision  of the mouse wheel (the z and w coordinates).  This precision manifests itself as a
       multiplier on the dz and dw fields in mouse events.  It also affects the z and w  fields  of  events  and
       ALLEGRO_MOUSE_STATE(3alleg5),  but  not  in  a  simple  way  if  you  alter the precision often, so it is
       suggested to reset those axes to 0 when you change precision.  Setting this to a high value allows you to
       detect small changes in those two axes for some high precision  mice.   A  flexible  way  of  using  this
       precision  is  to  set it to a high value (120 is likely sufficient for most, if not all, mice) and use a
       floating point dz and dw like so:

              al_set_mouse_wheel_precision(120);

              ALLEGRO_EVENT event;
              al_wait_for_event(event_queue, &event);
              if (event.type == ALLEGRO_EVENT_MOUSE_AXES) {
                double dz = (double)event.mouse.dz / al_get_mouse_wheel_precision();
                /* Use dz in some way... */
              }

       Precision is set to 1 by default.  It is impossible to set it to a lower precision than that.

       al_set_mouse_wheel_precision - Allegro 5 API

al_get_mouse_wheel_precision(3alleg5)

Allegro reference manual                                                   al_set_mouse_wheel_precision(3alleg5)

       5.1.10

              #include <allegro5/allegro.h>

              void al_set_mouse_wheel_precision(int precision)