Two methods of simulations are described: an exact one - transfer matrixtechnique and a statistical one - Monte Carlo method. Both of them areapplied to investigate critical properties of classical spin models. To do thiswe also exploit finite size scaling and the critical point ratio of the squareof the second moment of the order parameter to its fourth moment. Generaldefinition of a classical spin model as well as particular definitions ofmodels are presented. Results of both methods are in good agreement and,moreover, they are consistent with numerical results provided by literature.