  A quantitative method is presented to compare observed and synthetic
colour-magnitude diagrams (CMDs). The method is based on a chi^2 merit function
for a point (c_i,m_i) in the observed CMD, which has a corresponding point in
the simulated CMD within n*sigma(c_i,m_i) of the error ellipse. The chi^2 merit
function is then combined with the Poisson merit function of the points for
which no corresponding point was found within the n*sigma(c_i,m_i) error
ellipse boundary. Monte-Carlo simulations are presented to demonstrate the
diagnostics obtained from the combined (chi^2, Poisson) merit function through
variation of different parameters in the stellar population synthesis tool. The
simulations indicate that the merit function can potentially be used to reveal
information about the initial mass function. Information about the star
formation history of single stellar aggregates, such as open or globular
clusters and possibly dwarf galaxies with a dominating stellar population,
might not be reliable if one is dealing with a relatively small age range.
