  The measure-multiplicity-invariant for masas in $\rm{II}_{1}$ factors was
introduced in \cite{MR2261688} to distinguish masas that have the same
Puk\'{a}nszky invariant. In this paper we study the measure class in the
measure-multiplicity-invariant. This is equivalent to studying the standard
Hilbert space as an associated bimodule. We characterize the type of any masa
depending on the left-right-measure using Baire category methods (selection
principle of Jankov and von Neumann). We present a second proof of Chifan's
result on normalisers and a measure theoretic proof of the equivalence of weak
asymptotic homomorphism property (WAHP) and singularity that appeared in
\cite{MR2417416}.
