  Expanding laser plasmas, produced by high energy laser radiation, possess
both high thermal and magnetic field energy density. Characterization of such
plasma is challenging but needed for understanding of its physical behaviour.
Among all standard experimental techniques for plasma diagnostics, classical
interferometry is one of the most convenient, informative and accurate.
Attempts to extract more information from each single laser shot have led to
development of complex interferometry, which under certain processing allows to
reconstruct both plasma electron density and magnetic field strength
distributions using just one data object. However, the increase in complexity
and universality of the diagnostics requires a more detailed analysis of the
extracted values and their accuracy.This work focuses on axisymmetric
interaction geometry. We present general analysis, starting from the basic
principles and trace main error sources, finally ending up with plasma density
and magnetic field distributions with the derived error bars. Use of synthetic
profiles makes the analysis universal, though we present an example with real
experimental data in the Appendix.
