/******************************************
 * calculable textfield
 *
 * usage: $('.calculable').calculable();
 ******************************************/
(function ( $ ) {
	$.fn.calculable = function()
	{
		this.keydown(function(event){
			if ( event.which === 61 ) { //keycode 61 is the equals sign =
				var string		= $(this).val().replace(',','.').replace(/[^0-9.+\-\/\*]/g,'');
				var calculated	= eval(string);
				if(typeof calculated !== 'undefined') {
					$(this).val(calculated);
				}
				event.preventDefault();
			}
		});
		return this;
	};
}(jQuery));