An assay device with an assay result reading device for reading the result of assays performed on the assay device, the assay device being for determining the presence and/or extent of one or more analytes in a liquid sample, said assay device comprising: a) first and second assay test strips (22,23) each comprising a respective flow-path having a detection zone (24,26) 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, wherein the first and second assay test strips are on separate substrates or provided on a common substrate but isolated in such a way that liquid cannot cross from the flow-path of one assay test strip to the flow-path of the other, and wherein the first and second assay test strips have a common porous sample application region; b) a single, shared reference zone present on one of said first and second assay test strips, and a single, shared control zone present on one of said first and second assay test strips; the assay result reading device comprising: c) one or more light sources (41,45) to illuminate the detection zones, the shared reference zone, and the shared control zone; d) one or more photodetectors to detect light from the detection zones, the shared reference zone, and the shared control 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; wherein the value of the signal obtained from the shared reference zone on one of said assay test strips is used to compensate the value of the signal obtained at the detection zone of the other of said assay test strips, and the measurement of the signal from the shared control zone provides an indication whether or not a test has been carried out correctly for the assay. a) first and second assay test strips (22,23) each comprising a respective flow-path having a detection zone (24,26) 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, wherein the first and second assay test strips are on separate substrates or provided on a common substrate but isolated in such a way that liquid cannot cross from the flow-path of one assay test strip to the flow-path of the other, and wherein the first and second assay test strips have a common porous sample application region; b) a single, shared reference zone present on one of said first and second assay test strips, and a single, shared control zone present on one of said first and second assay test strips; the assay result reading device comprising: c) one or more light sources (41,45) to illuminate the detection zones, the shared reference zone, and the shared control zone; d) one or more photodetectors to detect light from the detection zones, the shared reference zone, and the shared control 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;