Nature of crossover from classical to Ising-like critical behavior

We present an accurate numerical determination of the crossover from classical to Ising-like critical behavior upon approach of the critical point in three-dimensional systems. The possibility of varying the Ginzburg number in our simulations allows us to cover the entire crossover region. We employ these results to scrutinize several semiphenomenological crossover scaling functions that are widely used for the analysis of experimental results. In addition, we present strong evidence that the exponent relations do not hold between effective exponents.