You can control the temperature either by typing a (positive) real number into the temperature field or by adjusting the thermometer by mouse. To set the critical temperature T_Crit=2/ln(1+sqrt2) of the 2 dimensional Ising model (which is connected with a phase transition on the infinite lattice) click on the corresponding symbol. Every little box of the spin field represents one of the two possible states S_i=-1, 1 (white/blue).

The Hamiltonian is calculated by the formula H=Sum_<i,j>S_iS_j where <i,j> symbolizes all pairs of next neighbours on the lattice. The magnetization is simply the mean of all spins.