 However, nearly any probe of folded structure will work; since the measurement is taken at equilibrium, there is no need for high time resolution.Thus, measurements can be made of NMR chemical shifts, intrinsic viscosity, solvent exposure (chemical reactivity) of side chains such as cysteine, backbone exposure to proteases, and various hydrodynamic measurements.To convert these observations into the probabilities formula_13 and formula_14, one generally assumes that the observable formula_41 adopts one of two values, formula_42 or formula_43, corresponding to the native or unfolded state, respectively.