function changeFontSize( objId, doIncreaseSize ) {
//Define your variables before use, or they will become global.
    var currentSize = 0, 
		obj = document.getElementById( objId ), 
		newVal = 0, 
		limitMax = 2, 
		limitMin = 0.5, 
		unit = 0.1; 

	if( !obj ){
	 return false; //Avoids errors if obj isn't found.
	}
    currentSize = parseFloat( obj.style.fontSize );
	if( doIncreaseSize ){
		unit = -unit; // unit becomes negative. This turns subtractions into addition.
	}
	newVal = currentSize - unit;
	if( limitMax >= newVal && limitMin <= newVal ){
		obj.style.fontSize = newVal + "em";
	}
};