Paralax

When I look through most of my rifle scope there is one locatin where I can place my eye and slight movement does not change point of aim.
I have one scope from a top brand that I am unable to locate this sweet spot. No matter where I place my eye slight movement changes point where croos hairs are located on target. How can I tell if a replacement socpe will be better by reading specifications? I guess I got lucky on the other scopes I have!
Tim

Riflescopes are almost always set to be parallax free at 100 yards. Leupolds are 150. Shotgun scopes are 60 or 75. Other types of scopes may differ, but this covers most. You may actually be off by some yards, but it is really a moot point. Makes no difference by such a slight change. You also can't check with your gun on a rifle unless it is in a fixture. You can't hold it and determine this.