function show(x, y) {
  document.write("<tr><td>" + x + "<td>" + (x+y-x));
}

document.write("<table border>");
document.write("<tr><td>X<td>X+1000-X");

show(1e9, 1000);
show(1e18, 1000);
show(1e27, 1000);

document.write("</table>");