[en] The Posiva Flow Log, Difference flow method (PFL DIFF) uses a flowmeter that incorporates a flow guide and can be used for relatively quick determinations of hydraulic conductivity and hydraulic head in fractures/fractured zones in cored drillholes. This report presents the principles of the method and the results of measurements carried out in drillholes OL-KR51, OL-KR52, OL-KR52B, OL-KR53 and OL-KR53B at the Olkiluoto investigation site between August 2009 and February 2010. The measuring programme employed was the same in all drillholes. The section length of the flow guide was either 2 m or 0.5 m. Flow into the drillhole or from the drillhole to the bedrock was measured within the section lengths and carried out in both pumped and natural (i.e. un-pumped) conditions. Calculations of the transmissivity (T) and the hydraulic head (h) of the zones are shown in the results. The device used includes a sensor for single point resistance (SPR). SPR was measured in connection with flow measurements. The electrical conductivity (EC) of fracture-specific water was measured in chosen fractures. Fractures were selected on the basis of the measured flow from fracture to drillhole. The drillhole flow (flow along the drillhole) was measured in conjunction with drillhole EC measurements. (orig.)