A zoomIn button

[Doug Nebert]

I am puzzled at making a zoomin button based on the current 
mapextent, being a javaScript newbie. With Steve's direction 
I have a nice button that will zoom to full extent:

    function goGlobal() {
        document.mapserv.imgext.value = "-180 -90 180 90";
        document.mapserv.imgbox.value = "-1 -1 -1 -1";
        document.mapserv.imgxy.value = "249.5 124.5";
        document.mapserv.zoom = "1";
    }

that I set with:

<input type="button" value="Zoom to Globe" onClick="goGlobal()">

and invoke with the submit effects of the form submission button. 
I need the similar functionality to place on twoi buttons with a 
pre-defined zoom in or out of 3 or -3 respectively.  I cannot quite 
decode the things being set in the form example I started with, but 
interpreted the following that does not work, gives a JS error:

    function zoomIn() {
        document.mapserv.layer = "registry";
        document.mapserv.zoom = "3"
        SetZoomToPan();
        SetModeToBrowse();
    }

Assistance appreciated.

-- 
Douglas D. Nebert
Clearinghouse Coordinator 
FGDC Secretariat	Phone: +1 703 648 4151	Fax: +1 703 648-5755	
Pager Messaging: 	http://fgdclearhs.er.usgs.gov/dougmsg.html