For fuel-motion surveillance in Transient Reactor Test Facility experiments, the fast-neutron hodoscope has advanced beyond its initial ability to provide time, location, and velocity data: its quantitative mass results are now routinely used in liquid-metal fast breeder reactor accident projections. (Mass normalization is based on initial fuel inventory.) The material and radiation surroundings of the test section affect hodoscope detectors in intrinsic and instrumental ways that necessitate detailed corrections. Depending on the experiment, count rate compensation with as little as 5% total imprecision is usually desired for dead time, power-level changes, nonlinear response, efficiency, and background. In addition, systematic effects ranging up to 20% may occur, from such causes as self-shielding, self-multiplication, self-attenuation, and flux depression. For one- to seven-pin bundles, the hodoscope has achieved 1-ms time resolution, 0.25-mm lateral- and 5-mm axial-motion displacement detection, and 50-mg single-pin, 350-mg seven-pin mass resolution—not all, however, simultaneously, since resolution and statistical precision are inversely related. The experimental and theoretical foundation for that performance is now well established.