Well I have a tricky story for ya. I just put in a 4x in my viper and a couple of different people told me I would have to adjust my sight. The day I put it in I was spot on, no adjustment needed that I could tell. The next day I shot again with the same results. The day after that I shot my league inside at paper and couldn't a darn thing. So, I started moving things. Long story short, I don't have the lens in it any more, and had to resight my bow back in from where I moved it. I will put the lens back in but for now, the next couple of shoots I am going to I am shooting in the novice class and can't use it anyway. So when I am ready to move back to the hunters class I will put it back in and leave it in from then on but only after I adjust my sight.