The change of picture in approximate two-component relativistic theories: Expectation values of r, r(-1) and r(2)

The change of picture for operators which arises in approximate two-compone nt relativistic theories is analysed formally and exemplified by the evalua tion of relativistic corrections to the distance operator, its square, and its inverse. The change of picture contribution to the expectation value of the distance operator is interpreted as an error arising from the use of o perators in what is called the Schrodinger picture. This is at variance wit h earlier interpretations of this contribution.