Time traveling in the DeLorean is accomplished in three steps. In the first, he traveler turns on the “time circuits” using a rocking switch in the central console. Its use is detailed in the original Back to the Future, as below.
In the second, the traveler sets the target month, day, year, hour, and minute using a telephone keypad mounted vertically on the dashboard to the left, and pressing a button below stoplight-colored LEDs on the left, and then with an extra white status indicator below that before some kind of commit button at the bottom.
In the third, you get the DeLorean up to 88 miles per hour and flood the flux capacitor with 1.21 gigawatts of power.
Note that the rocker switch angles down to a nearly 45 degree angle in the on position. One of the worst thing that could happen is for that thing to get accidentally turned off at the wrong time, I imagine. (Back to the Future 4: Lost in Somewhen?) The 45 degree angle makes an accidental activation unlikely, but the T-shaped handle means it could catch on a sleeve or bag handle or something. There are more secure safety switches, but I also wonder if it would be smarter to use the Fake Off mode that most electronics run in today, where they’re never really off, but look off, just waiting for user interaction to spring to life. With a Mr. Fusion on board, I presume powering it isn’t that much of a problem.
Note that the pad only has numbers. But Doc uses the military and European standard date format
[day of month] [month] [year]
which might confuse another user, i.e. Marty, entering the stupid USA standard
[month] [day of month] [year]
Though preventing errors is preferable, at least Doc helps Marty recognize errors by displaying the month in 3-character text format, which would help Marty realize if he’d accidentally put in 10 September instead of 09 October.
Note that doc is traveling to 4:29 in the afternoon, and the display has a tiny LED A.M./P.M. indicator. Better is the less ambiguous military time. Sure, audiences might have been confused, but using a 24-hour clock would have been less ambiguous for diegetic users, you could eliminate the AM/PM indicator, and Doc could use the existing number pad for entry without having to either add an “AM” and “PM” button (missing from the console), or doing some annoying “press 1 for AM or 2 for PM now” IVR thing.
While we’re on time disambiguation, what, uh, time zone is this? Did doc only ever plan to fly in and around Hill Valley? It might have been keyed to the Prime Meridian, or to Pacific Time, but if so it would have been very useful to have it marked as such. If not, it should display the current time zone and provide a means to change it. Somehow. With that number pad. (Or more controls.)
Bad input constraint and recovery
It’s wholly possible to enter a day-of-month or month of “99,” which is nonsensical given the Gregorian calendar that we use today. How does the system handle this? A mod function? There’s no clue, but the unconstrained inputs would allow it.
As the Long Now Foundation reminds us, a four-digit date is really short-sighted. So Doc didn’t want to travel to 10,000 C.E. and see if Zager & Evans were right? And what if he wanted to go meet Amenhotep? How does he specify 1526 B.C.E.? It seems unduly constrained.
I don’t know what those LEDs to the left of the input panel do, but I can tell they’re poorly mapped. The colors go, from top to bottom: red, yellow, and green, like a stoplight. Then there’s the extra white LED below that maps to nothing. But the LED colors on the display go from top to bottom red for destination, green for present, yellow for last time departed. Better mapping would have these two agree, or distinct color schemes.
In 1985 dialing a telephone number worked much like the dial-a-date seen here. Punch a sequence of numbers and the system runs with the input. But instant-input systems need a way to correct errors; either the ability to review and correct the input, or to abort the input altogether and start over.
Phone users from back then will recall it was entirely possible to mistype a digit and dial a wrong number. You’d be connected to a stranger who had no idea who this “Marty” you wanted was. This is more serious in the DeLorean than on a phone, as it drops the user into circumstances potentially much more dire, from which there might be no recovery. What would happen if they had accidentally wound up in 21 October 1015? Wholly different story. Is Biff distantly related to Cnut the Great?
Doc might be able to review the input on the display before getting up to speed, but there’s no obvious control for aborting input so far and starting over. (What if he has skipped a digit instead of mistyping one?) A simple delete button would help him correct mistyped digits. Even if he mistyped the first one and only realized it at the end, it wouldn’t be too burdensome to press delete the handful of times.
How does the system confirm for Doc that he’s entered the right date he intended to? On one level, sure, the 7-segment LED output is clear and unambiguous. It’s a nice discrete number. But of course 7-segment 1989 isn’t that easy to distinguish from 1898 when you’re distracted. Better would be to give a preview of the meaning of the choices entered (but not yet enacted) by the user. If there was a video screen in the car, then maybe it could show scenes from old Westerns with the label “Headed to 1898: The Old West.” You could even do it with the cars’ speakers and an audio soundscape if a screen wouldn’t work for space or distraction reasons.
As noted in the overview, Biff(2015) gets into the car to make off for 1955 early in the film. I can’t quite figure out how he was able to figure out turning on the time circuit and that the 88MPH was a target speed, but he did. (Seriously, looking for fan theories here.) Of course Doc might have designed everything to be perfectly understandable for Marty, but that’s no excuse to avoid authenticating the user, since Doc is so panicked about the consequences of the time travel that he’s doing all the times. [sic]