Disclosed is an assay device for determining the presence and/or extent of one or more analytes in liquid sample containing a) first and second assays each comprising a flow-path having a detection zone for immobilising a labelled binding reagent, wherein detection of a labelled binding reagent at one or both detection zones is indicative of the presence and/or extent of one or more analytes; b) a shared reference zone; c) one or more light sources to illuminate the detection zones and the reference zone; d) one or more photodetectors to detect light from the detection zones and the reference zone, which photodetector/s generate a signal, the magnitude of which signal is related to the amount of light detected; and e) signal processing means for processing signals from the photodetector/s.