How to protect a chronograph screen
I have always used Oehler equipment since my first Model 10. The present 35 has had the screens modified to wider hoods, etc.
What I do is tape a piece of blank paper to the outside of the far hood bracket. I scribe a small dot in the appropriate position. Now, remember, there is considerable parallax between a scope or iron sights and the centerline of the bore. Take this into consideration.
But, the most important thing to remember is that you bought the machine and you are under no obligation to loan it out free to friends or casuals on your range. YOU do the shooting and let these el-cheapos buy their own equipment.
My best friend shot away the screens on my Model 10 many years ago and I'm still waiting for him to reimburse me for the damage he caused. It isn't a joke; a set of screens for the Oehler 35 cost $111, and some yahoo can blow them away with one shot.
My guns, my wife, my truck and my chronograph are mine exclusively (I'm never sure about my dog.)