I recently purchased a 40s or 50s vintage Mossberg M4D 4 power telescope. It is in beautiful condition, and the rubber eyepiece is like new. It is clear and required only a minor cleanup to look mint. It also has a Weaver 22 tip off mount and I planned to use it on one of two .22 rifles. On the foward end it has a small oval plate with a small common screwhead on it. The seller told me that it was to adjust parallax if any was present. He claimed he did not know how it worked however. I hope one of you that knows more than I do, can tell me if that is accurate and if so how do you perform that task. Secondly, can I remove the plate by removing the small screw so I can change the mount as it seemingly won’t come off without removing it. At 83 years of age I have learned not to screw around with things until I as least have some idea of what I am doing. That situation applys here. The little scope is in such good shape. If any of you can help me with this I would really appreciate it. Thank you in advance.............Catch