function graph_zoom(divId, svgId, scale) {
var pg = document.getElementById(divId);
vcenter = (pg.scrollTop + (pg.scrollHeight - pg.scrollTopMax)/2.0) / pg.scrollHeight;
function graph_zoom(divId, svgId, scale) {
var pg = document.getElementById(divId);
vcenter = (pg.scrollTop + (pg.scrollHeight - pg.scrollTopMax)/2.0) / pg.scrollHeight;