A large class of flow observables such as event-plane correlations and longitudinal de-correlations can also be measured at RHIC with possible future forward upgrades. These will help further elucidate the space-time picture of the QGP evolution in both the transverse and longitudinal directions. Together with the existing large set of published data on the event-averaged flow, these new measurements will enhance our understanding of QGP at 200 GeV and together with similar measurements at the LHC, will constrain the temperature dependence of the QGP properties.

What measurements at RHIC (particularly in the forward rapidity region) remain essential for the development and constraint of 3D hydrodynamics, and what capabilities are required to make those measurements?