[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-PP66, OL-PP67, OL-PP68 and OL-PP69 at the Olkiluoto investigation site in August 2008. All the drillholes discussed in this report are ground holes. The same measuring programme was employed in all four 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 in some of the drillholes. Fractures were selected on the basis of the measured flow from fracture to drillhole. The EC of the drillhole water was also measured. (orig.)