onMouseWheel?

#1 I don't think there is a callback for it. Access it using a bindCmd.

actionMap.bindCmd(mouse, "zaxis", "doMouseWheelFunction", "");

#2 You are correct. I'm getting close with this:

moveMap.bind(mouse0, zaxis, zoomMap);

But I need to distinguish between wheel forward / wheel back

It only sees one of the functions:

moveMap.bind(mouse0, zaxis, zoomMapOut, zoomMapIn);

And the bind command does not accept parameters like bndCmd:

moveMap.bindCmd(keyboard, "up", "$player.PlayerUp(1);", "$player.PlayerUp(0);");

#3 Ok dude...

moveMap.bind(mouse0, zaxis, "doMouseWheelFunction");  

function doMouseWheelFunction(%val)
{
   echo("mouse wheel moved:" SPC %val);
   
   if(%val > 0)
   {
      echo("Mouse moved forward");  
   }
   else if(%val < 0)
   {
      echo("Mouse moved backard"); 
   }
}

#4 Crazy! I never would have guessed:

Mousewheel forward: %val = 120
Mousewheel backward: %val = -120

Thus, this works:

moveMap.bind(mouse0, zaxis, zoomWheel);
...

function zoomWheel(%val)
{
   zoomMap(%val>0);
}

Thanks Patrick!

#5 I was curious if that value was device specific but I get 120/-120 as well. You're welcome!