function my_center(x,y,z)
{
bWidth=document.body.clientWidth;

x=(bWidth-x)/2;
y=(bWidth-y)/2;
z=(bWidth-z)/2;

if (x < 0){x=0};
if (y < 0){y=0};
if (z < 0){z=0};

M1.style.left=x;
M2.style.left=y;
M3.style.left=z;
}