By buying it I did not think monocular vision was so painful / difficult. It is not clear it is necessary to calibrate well and one quickly realizes that it is "tiring" to keep one eye closed. In the end I bought it but I think never use. Even my 5 year old daughter and a half has not wanted after trying 2 or 3 times. I frankly advise to buy a pair of binoculars or a monocular better quality of vision in this one is not good.