We present Sigma Web interface which provides user-friendly access for online
analysis and plotting of the evaluated and experimental nuclear reaction data
stored in the ENDF-6 and EXFOR formats. The interface includes advanced
browsing and search capabilities, interactive plots of cross sections, angular
distributions and spectra, nubars, comparisons between evaluated and
experimental data, computations for cross section data sets, pre-calculated
integral quantities, neutron cross section uncertainties plots and
visualization of covariance matrices. Sigma is publicly available at the
National Nuclear Data Center website at http://www.nndc.bnl.gov/sigma