For some circumstances, including the common T1-T2 measurement equilibrium magnetization and the preparation flip angle must determined from the data, the spectral matrix components , S  are not linearly independent. This leads immediately to a rank-deficient Fisher information matrix, or to unbounded covariances in its reciprocal. Though SVD analysis can identify interdependent parameters, it is also possible to examine the measurement protocol directly to see the origin of the parameter interdependencies. Doing this gives physical insight and defines a set of parameters that can be determined using ARM+LSQ and explored using Monte-Carlo calculations.