Thank you for the reply, I do know how to reduce parallax error by moving my head back and centering the image.

My question was more specifically what degree of error is introduced at 100 yards if parallax is adjusted to 250? and then how much improvement in parallax error does this result in at 500 yards? More simply, if one is going to shoot with equal frequency at 100 yards and 500 yards is the ideal place to set parallax 250 yards in order to minimize error at both the near and far range?

For the sake of accuracy in the above example- the scope would be a 1"tube 3.5-10x with 40mm objective

Thank you

If you can't be a good example, may you at least serve as a dreadful warning