•The blue curve in the image is the fitted curve by the Young-Laplace equation, the black part is the shape of the droplet, the red line is the edge points found by the software, and the horizontal line is the baseline;

•By zooming in on the Base line at the image, it can be easy found out that the blue fitting curve does not substantially coincide with the droplet contour (black part).

•It is easy to judge if the calculated value of contact angle  deviates from the actual value by the coincidence of the fitting curve and droplet edge. Moreover, since the fitted curve shrinks within the true edge of the droplet in this image, it can be judged that the calculated angle value is larger than the true value.