Psd acc. Is in say m/s2 units and the other is in g units 9.81 m/s2. Thus if you have 2 g units in g psd units, that is equivalent to 2*9.81 m/s2 in psd acc. So to go from acc. UNITS to g acc. units one divides by 9.81. The other way around to go from g units to m/s2.