function TextSize(temp)
{
var $mainText = $('#testo');
var currentSize = $mainText.css('font-size');
// parse the number value out of the font size value, set as a var called 'num'
var num = parseFloat(currentSize, 10);
// make sure current size is 2 digit number, save as var called 'unit'
var unita = currentSize.slice(-2);
if (temp == 'aumenta'){
num = num * 1.1;
} else if (temp == 'riduci'){
num = num / 1.1;
}

$mainText.css('font-size', num + unita);
   return false;
};