Quasi-2d square lattice magnets are good model systems to study 2d criticality due to several reasons. Many real system can be described by relatively simple Hamiltonians, they show pure 2d behavior in certain parts of the temperature-magnetic field phase diagram and several thermodynamic parameters can be well measured by neutron scattering (order parameter, correlation length) or bulk property methods (heat capacity, magnetic susceptibility). We propose to measure the 2d criticality of the XY model with 4-fold anisotropy. Our sample is Rb2CrCl4 a prominent realization of the 2d XYh4 model (XY anisotropy with 4-fold anisotropy in the easy plane). We propose to measure the criticality (magnetization and correlation length of the fluctuations) as a function of transverse magnetic field, that is expected to destroy the 3d fluctuations around the critical temperature Tc = 52 K.