    dd=M*dt/1e6;                  % time to delay
    if(dd>2)                      % feedback only for long pauses
      fprintf('Acquiring data for %3.1f seconds:',dd);
      nn=0;
      tic;
      while(s.BytesAvailable==0)
        pause(.05);
        if(10*toc>nn)
          if(rem(nn,10)==0);
            if(rem(nn,100)==0)
              fprintf('I')
            else
              fprintf('=');
            end
          end
          nn=nn+1;
        end
      end
      fprintf('Done.\n')
    end
