- "First, you turn the time circuits on."
- —Doc Brown explaining to Marty how the DeLorean time machine works.
Years were limited to four digits and there were no possible negative years that could be reached (i.e. years before 0 AD). This means the DeLorean could travel to any time from 12:00 am on January 1, 0000 AD to 11:59 pm on December 31, 9999 AD. It is unclear what would happen if one were to travel to the latter date since, after only one minute, it would be the year 10000 AD and the time display would therefore no longer be able to show the present time.
Doc Brown demonstrated its capabilities to Marty McFly after its first test, giving two well-known but erroneous dates as examples, the signing of the Declaration of Independence, July 4, 1776, and the birth of Christ, December 25, 0000. (In practice, these events could only be viewed by driving to the location of the event with the help of gas stations and freight ships, and then traveling back in time, since the DeLorean did not yet travel in space at this point in its construction.) Then, Doc Brown gave a third example by setting them to the day that he invented time travel, November 5, 1955. Because Doc only set a day, month, and year, the time defaulted to 6:00 a.m.
The setup was apparently user-friendly considering that Marty and Biff Tannen were both able to insert destination times quickly and easily. In order to enter a date and time, one pressed digits on the keypad in the order that they would be displayed, and then press the activation button. For example, to set the time to November 5, 1955 at 9 a.m., one would press 110519550900 and hit ENTER. In order to add time in the afternoon of a date, the operator would likely have keyed 1300, 1400, etc., to represent 1 p.m. and 2 p.m., respectively.
After the trip to 2015, the time circuits began malfunctioning, displaying "Jan 01, 1885", at midnight, in the destination slot in mid flight. A bolt of lightning triggered the malfunction to send the DeLorean from 1955 to 1885. Though the vehicle was in mid-air, the spin created by the lightning bolt allowed it to reach 88 mph.
After the Delorean falls from a billboard in 1986B, the time circuits cease to function altogether. Though Citizen Brown would repair them, the best he could, the time circuits would fail to take the Delorean to its exact destination. Following examples include:
- Citizen Brown arriving to the Courthouse Square 2 minutes after his departure when he intended it to be exactly after he departs.
- Marty and Citizen Brown arrive in October 12, 1931 rather than August 26, 1931.
After the time machine was rebuilt by Doc in 1991, the time circuits were constructed to be voice-activated, as well as being coupled with a device that allowed spatial displacement. It appears that the circuits could now display year numbers larger than 10,000.
Behind the scenes
- The Time Circuit display undergoes a slight change between Back to the Future Part I and Part II. In Part I, the "AM/PM" light has AM on top and PM on the bottom. In Part II and onwards, PM is on top while AM is on the bottom. It is unknown if this was simply a movie error or if Doc, for some reason, decided to change it upon upgrading the car in the future.
- Back to the Future Trilogy
- Back to the Future: The Animated Series
- Back to the Future Part II & III
- Back to the Future: The Game