func OnLineHeader () {
        output(LH);
}
func OnTrace () {
                a = Tr.SrPtXC;
                b = Tr.SrPtYC;
                c = Tr.RcPtXC;
                d = Tr.RcPtYC;
                e = 0.5*(a+c);
                f = 0.5*(b+d);
                Tr.SrRcMX = e;
                Tr.SrRcMY = f;
                output(Tr);
}
func End(){
print (" end of midpoint ufh \n");
}