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Message: <blockquote data-quote="Surveyor" data-source="post: 1649406" data-attributes="member: 50720">RonH;I have seen the effect, though not used it for IPD. Yes, your assumptions are correct about square ness in both cases.In surveying lingo, this is referred to as auto-reflection and used where the precision of auto-collimation is not required. We use a glass with an etched cross hair on the objective as the reflection target to square the instrument.One thing that may improve your results and time taken. Try using a cardboard baffle to separate your eye lines so your right eye does not see the left mirror image and vice-versa.Bob (ceaser);Yes, I pretty much do it whenever I get a bino out. I use 6x, 7x or 8x20’s most of the time, double hinge, and find it faster to take a scale and set (as a surveyor, I always have a scale in my pocket) the IPD rather than trying to set by feel. On my larger binos, I very seldom use a case, so once set, they stay set but I will check them occasionally. If testing, I always set by gauge prior to the test. I also have placed threads on the bino straps of several binos at my IPD for the purpose.From my perspective, I think it is faster and more positive.Kimmo,Some time later today I will send you an email. You may make a good guinea pig for describing what I need in the way of digital photos for measuring your IPD by photogrammetry and seeing how the results compare to other methods if interested.BestRon</blockquote>