Here you can plot the points of an elliptic curve under modular arithmetic.
Enter the curve parameters and press 'Draw!' to get the plot and a tabulation of the point additions on this curve.
Note: Since it depends on multiplicative inverses, EC Point addition will only work for prime moduli like 2,3,5,7,11,13,17,19,23,29,31,...,109,... ;-)
(c) Sascha Grau, 2011