  This paper is a first step towards developing a formalism to optimally
extract dark energy information from number counts using multiple cluster
observation techniques. We use a Fisher matrix analysis to study the
improvements in the joint dark energy and cluster mass-observables constraints
resulting from combining cluster counts and clustering abundances measured with
different techniques. We use our formalism to forecast the constraints in
Omega_{DE} and w from combining optical and SZ cluster counting on a 4000 sq.
degree patch of sky. We find that this cross-calibration approach yields ~2
times better constraints on Omega_{DE} and w compared to simply adding the
Fisher matrices of the individually self-calibrated counts. The
cross-calibrated constraints are less sensitive to variations in the mass
threshold or maximum redshift range. A by-product of our technique is that the
correlation between different mass-observables is well constrained without the
need of additional priors on its value.
