  Considering a minimal number of assumptions and in the context of the
timeless formalism, we derive conditional probabilities for subsequent
measurements in the non-relativistic regime. The probability expressions are
found unambiguously, also in puzzling cases like the Wigner's friend scenario,
and they underline the relativity aspect of measurements. No paradoxical
situations emerge and the roles of Wigner and the friend are completely
interchangeable. In particular, Wigner can be seen as a superimposed of states
from his/her friend. When only one clock system is considered, we demonstrate
in addition that two-times probabilities cannot be defined.
