We propose to investigate the field induced behaviour of ErB4 using WISH. ErB4 is an example of experimental realisation of the Shastry-Sutherland lattice, a frustrated lattice that has an exact ground state solution. Competition between the magnetic and quadrupolar interaction is believed to be crucial in establishing a ground state, leading to fractional magnetisation plateaux and complex phase diagrams. Our recent diffraction experiments on other two members of the family, HoB4 and NdB4 have shown that surprisingly the field evolution of the magnetic structures in these compounds (corresponding to 1/3 and 1/5 magnetisation plateaux) involves rearrangements of the magnetic moments in the neighbouring planes. We aim to establish the magnetic structure of ErB4 in fields corresponding to the 1/2 magnetisation plateau. We have grown and characterised large single crystal samples of ErB4.