To beign, take your pop-up sprayer sprinkler and unscrew the top cap.  Pull out the internals.  Pull down on the cap, squeezing the spring, and unscrew the sprayer cap on the end of the shaft.  Take out the clear plastic (or whatever color it is) cone-shaped filter while you're here.  Now, let go of the top cap (don't point it at anyone, as it will fly off.)  Remove the spring, and any other plastic parts from under, above, or around the spring.  You should have a bare central shaft.  Look down it, from the fatter end.  It's your scope.  Electrical tape it down to the gun you want it on (the one I used for the pictures is a perfect size for a pistol; bigger ones are out there that are excellent for rifles, etc.)  Once it is attached, calibrate it (test fire the gun for accuracy and re-adjust the scope's alignment as necessary) and then apply hot glue underneath the electrical tape to secure it in its calibrated location (only on one end, so you can make last-minute corrections.)  You're ready to go, and MAN it looks good...