Why is the animation duration of jquery's animate function inconsistent? -

please have @ these simple jquery animations:

animate.mouseenter(function () {     animate.stop().animate({ opacity: 0 }, duration); });  animate.mouseleave(function () {     animate.stop().animate({ opacity: 100 }, duration * 10); }); 

my questions:

• why animation time of these 2 animations more or less equal, although duration multiplied 10 mouseleave animation?
• is there particular reason behavior?
• is factor 10 or other floating point value close 10?

here working fiddle: http://jsfiddle.net/tcmjd/3/

i added example of fadeinand fadeout functions, equal duration parameters yield equal animation times should be.

because opacity of 1 opaque. you're animating way 100, hits 1 pretty quickly.

http://jsfiddle.net/e8n4q/

var animate = $(".animate"), fade = $(".fade"),  duration = 500;  animate.mouseenter(function () {     animate.stop().animate({ opacity: 0 }, duration); });  animate.mouseleave(function () {     animate.stop().animate({ opacity: 1 }, duration * 10); });  fade.mouseenter(function () {     fade.stop().fadeout(duration); });  fade.mouseleave(function () {     fade.fadein(duration * 10); });