I own a Redfield spotting scope the model year is between the 70's to 80's and I need to find a manual for it. But I was Wondering if you could answer a question there is a crossair, then there is another one right above that, then there is a loop on the bottom right hand corner. There is also a yard marker that starts at 600 and goes down to 100. Do you know what it is and how to use it or what the purpose of it is if you could help me that would be great. Thank you for all your help..Joshua Gambler