Single entities such as fibers are delivered one at a time to a fluid stream, and a nozzle orients the entities so that each entity along its length (major dimension) is generally parallel with the direction of fluid flow. The entity then enters a sample region and a sensor senses entity data such as the speed of the entity as it passes through the sample region. A preferred embodiment includes a collimated beam of light and two side-by-side photo detectors positioned to measure light extinction caused by fibers passing through the sample region. Another sensor may be provided to detect light scattered forward at an angle of about forty degrees (40.degree.). The sensor signals are used to generate data that corresponds to such parameters as length, fiber ribbon width, fineness, cross-sectional area, maturity, cross-sectional circularity, shape, surface roughness, etc. Optical filtering provides information about composition (natural or man-made) and appearance (color and polarization).