In this Note the reheat thrust boost for a turbo-jet engine is shown to depend upon various dimensionless parameters, one of which is engine pressure level. The importance of this ratio is illustrated graphically and it is shown to be most important over the range normally encountered on a test bed. It is shown that a given reheat system would deliver a higher thrust boost on a high pressure level engine than it would on a low pressure level engine. Finally, the pressure level effect on the thrust from an engine having a reheat system fitted but operating with the reheat unlit is discussed.