Kahles 3-12x56

I have had this scope for almost 30 years and recently moved to to another rifle. Unfortunately, I no longer have the instructions manual and after I sight in the scope, it doesn't stay sighted in.

Does anyone have one of these scopes or the manual. The adjustment knobs have another small screw on the edge of the ring.

On my other scopes, this is usually to allow you to change to knob without changing the POA to set the adjustment to '0', but on this scope there are no markings to define a '0'.

I was thinking that the reticle doesn't lock in until the set screws are set to make the change permanent, but don't know.

Thanks in advance.