The Gale-Zemeckis coordinate system allows every time period on Earth to be represented by a set of numbers or symbols.
In 1991, Emmett Brown built an 8-passenger DeLorean time machine that used Gale-Zemeckis coordinates to calculate time periods which could not be represented by the four-digit year system that was used by the time circuits.
Later that year, Doc traveled to 2015 to explain how changing the past can have repercussions on the time stream. Biff Tannen's stealing the DeLorean time machine to travel to 1955 to give his younger self a Grays Sports Almanac was used as an example. He then showed a Gale-Zemeckis diagram which demonstrated the temporal changes.
Behind the scenes
- The Gale-Zemeckis coordinate system was named after Bob Gale and Robert Zemeckis respectively, who directed and co-wrote all the installments in the Back to the Future trilogy.