Insert water level mark
 
    File name : WATERM.LSP

   Pick two points. Even though two point have diffent level.
Program draws level line referecing level of first pint.
Progrm inserts '\BLOCKS\WATERM.DWG' as a block. 
You can change mark or modify the file.
 
 Example
Pick first point: {p1}  [Pick first point]
Pick second point: {p2} [Pick second point]
                                Program ignores y-coordinate of point p2.
Pick insert point: {p3} [Pick insertion point of water mark. y-coordinate of this point is ignored]