  The online data reduction service reductus transforms measurements in
experimental science from laboratory coordinates into physically meaningful
quantities with accurate estimation of uncertainties based on instrumental
settings and properties. This reduction process is based on a few well-known
transformations, but flexibility in the application of the transforms and
algorithms supports flexibility in experiment design, supporting a broader
range of measurements than a rigid reduction scheme for data. The user
interface allows easy construction of arbitrary pipelines from well-known data
transforms using a visual dataflow diagram. Source data is drawn from a
networked, open data repository. The Python backend uses intelligent caching to
store intermediate results of calculations for a highly responsive user
experience. The reference implementation allows immediate reduction of
measurements as they are recorded for the three neutron reflectometry
instruments at the NIST Center for Neutron Research (NCNR), without the need
for visiting scientists to install additional software on their own computers.
