I use several types, the flip open style with my cheat sheets taped to them, and mounted so they flip open to opposing sides and I can still see over the scope. Depending on weather,rain, snow, fog whatever I have a couple sets of the clear see thru type. I have also made some bikini style out of inner tube, with a long tab on the close end, when ready to shoot just pull the tab back and let'er fly, pops right off. I made these so if they get lost no big deal.
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The good Lord gives us "Life" a "Window Of Opportunity" what we do with this opportunity, defines who we are and what we become.