LiHoxY1-xF4 in an applied transverse field was shown to be a realization of the Random Field Ising Model (RFIM),

in both its ferromagnetic and spin glass phases. We predict explicitly the random field in weak and strong

transverse fields using exact numerical diagonalization of the full Hamiltonian of 2 Ho ions. We then suggest

a direct measurement of the random field through sub-Kelvin co-tunnelling experiments.