  We show that the general Heisenberg Hamiltonian with non-uniform couplings
can be characterised by mapping the entanglement it generates as a function of
time. Identification of the Hamiltonian in this way is possible as the
coefficients of each operator control the oscillation frequencies of the
entanglement function. The number of measurements required to achieve a given
precision in the Hamiltonian parameters is determined and an efficient
measurement strategy designed. We derive the relationship between the number of
measurements, the resulting precision and the ultimate discrete error
probability generated by a systematic mis-characterisation, when implementing
two-qubit gates for quantum computing.
