Dizzib’s Earth Curve Calculator is one of the most popular Earth’s curvature calculator on the Internet. However, it does not account for atmospheric refraction and, therefore, unsuitable for determining the visibility of a distant object.
Many flat-Earthers used Dizzib’s calculator to analyze the observation of the visibility of a distant object and led them to an erroneous conclusion. If we can spot the calculator being used in their images, we can easily rule out their conclusion.