How to use a mirror stereoscope 

1. Sit directly in front of the midline of the stereo image

2. Hold the stereoscope up in front of your eyes

3. Close one eye and adjust the outer mirror so the disc image from the same side is central in the view from the open eye

4. Close the other eye and make the image on the same side as the open eye central by adjusting the outer mirror on that side

5. With both eyes open you should now have a stereo image

6. You may need to move closer or further away from the screen for the best stereo effect