program signal_receiver_bar
      real bar_x(5),bar_y(5)
      real bar_xold(5),bar_yold(5)

      x=5.0
      xmin=0.0;xmax=10.0;ymin=0.0;ymax=10.0;
      i_dummy=pgopen('/xwin')
      call pgenv(xmin,xmax,ymin,ymax,1,-1)
      call pgsfs(2)
 1000 open(unit=10,file='signal.txt',status='old')
      read(10,*)sig
      close(10)

      bar_x(1)=x+(-1);bar_y(1)=sig+(1);
      bar_x(2)=x+(+1);bar_y(2)=sig+(1);
      bar_x(3)=x+(+1);bar_y(3)=sig+(-1);
      bar_x(4)=x+(-1);bar_y(4)=sig+(-1);
      bar_x(5)=bar_x(1);bar_y(5)=bar_y(1);

      call pgbbuf
      call pgsci(0)
      call pgline(5,bar_xold,bar_yold)
      call pgsci(1)
      call pgline(5,bar_x,bar_y)
      call pgebuf

      do i=1,5
        bar_xold(i)=bar_x(i);bar_yold(i)=bar_y(i);
      end do

      goto 1000
      end