  We study uncertainty and certainty relations for two successive measurements
of two-dimensional observables. Uncertainties in successive measurement are
considered within the following two scenarios. In the first scenario, the
second measurement is performed on the quantum state generated after the first
measurement with completely erased information. In the second scenario, the
second measurement is performed on the post-first-measurement state conditioned
on the actual measurement outcome. Induced quantum uncertainties are
characterized by means of the Tsallis entropies. For two successive projective
measurement of a qubit, we obtain minimal and maximal values of related
entropic measures of induced uncertainties. Some conclusions found in the
second scenario are extended to arbitrary finite dimensionality. In particular,
a connection with mutual unbiasedness is emphasized.
