  Measurements in the quantum domain can exceed classical notions. This
concerns fundamental questions about the nature of the measurement process
itself, as well as applications, such as their function as building blocks of
quantum information processing protocols. In this paper we explore the notion
of entanglement for detection devices in theory and experiment. A method is
devised that allows one to determine nonlocal quantum coherence of
positive-operator-valued measures via negative contributions in a joint
distribution that fully describes the measurement apparatus under study. This
approach is then applied to experimental data for detectors that ideally
project onto Bell states. In particular, we describe the reconstruction of the
aforementioned entanglement quasidistributions from raw data and compare the
resulting negativities with those expected from theory. Therefore, our method
provides a versatile toolbox for analyzing measurements regarding their
quantum-correlation features for quantum science and quantum technology.
