function showTip(tip) {
    if (document.getElementById && document.getElementsByTagName) {
        var tipSection = document.getElementById('tools');
        var tips = tipSection.getElementsByTagName('div');
        for (var i=0; i<tips.length; i++) {
            tips[i].style.display = (i == tip ? 'block' : 'none');
        }
    }
}