<form method="post" action="#">
 <fieldset>
 <span id="number">100</span>
 <button> 25</button>
 <button>-20</button>
 <button> 375</button>
 <button>-210</button>
 </fieldset>
</form>​

var number = $('#number');
 
$('button','form').on('click', function(){
 
 var prevVal = parseInt(number.text()),
 newVal = parseInt($(this).text())
 
 /* start a dummy animation */
 number.animate({'z-index':number.css('z-index')},{
 /* declare a "step" function that will get executed at each step */
 step: function(now,fx){
 number.text( prevVal Math.floor( newVal*fx.pos ) )
 }
 })
 
 return false
})​