Abstract: To measure the volume of fluid that has flowed past a point and to actuate a sampler at certain increments of this volume, a stylus of a flow meter moves to a distance from the center of rotation of a rotating function disc, which distance is related to the height of a float in the fluid stream, with the function disc including a conductive portion having different arcuate lengths at different distances from the center of rotation so that, as the disc rotates, the stylus circumscribes a circle around the function disc at a distance related to the height of the float and is in contact with the conductive portion for a period of time that represents the rate of flow of the fluid that corresponds to the height of the float.