I notice that when I Zoom In/Out by MouseWheel the MapScale is not always increase/decrease by 2 times, this cause sometimes the MapScale is not in the Scales I set in publish titled service and titled image will distortion, Do you know how to solve this problem? thanks
There's never any guarantee that 2x is the zoom amount. If you mouse-wheel twice, and the first zoom isn't completed yet, it'll be 2x from where you started the next zoom. Also when you reach the min/max scale limits of the map, the zooming will also stop.