 "Significant Tornadoes" contains 51 photographs of tornadoes prior to 1970, the most extensive collection published.Grazulis amassed one of three authoritative tornado databases, those being the National Tornado Database assembled and maintained by NOAA agencies, the University of Chicago DAPPL database founded by Fujita which ended at his retirement in 1992, and the Grazulis Tornado Project database.As of 2014, the Grazulis database spans from 1680-1995 and includes all known significant tornadoes (those rated F2-F5 or causing a fatality).