Someone asked for this:
1. Extend your arm horizontally to its full length in front of you with your thumb pointed up to the sky. 2. with both eyes open and head still, site on an object in the nearby visual field, 2-4 meters is best, longer is more difficult, shorter less telling. 3. as you line up the thumb and object, focus on the thumb, leaving the object in the background to defocus. 4. When this is done, you’ll find by closing one eye at a time, that only one of your eyes is still sited on the target, and the other is not. 5. Now knowing your favored eye, and to paraphrase the use instructions on some chopstick packaging, “You can see anything!”