This achievement can be claimed when you reach a geohash on the correct day and return to your starting point without ever crossing your own tracklog. (The intention being that it might make for interesting detours and awkward route planning to accomplish.)
In the "Light Cycles" game popularized by the film TRON, players (and computer opponents) ride motorcycle-like vehicles in an arena. The bikes cannot stop, and constantly leave a trail, a glowing wall, along their path; the game's objective is to avoid crashing into these walls as long as possible (and to trick other players into crashing themselves).
In this achievement, the track log (breadcrumb trail) recorded by your GPS (if you have one, which is encouraged) acts as your wall trail, and your bicycle (or other mode of transportation, but bikes would be the most fitting) acts as the light cycle. To claim the achievement, you have to ride from your starting point (most likely your home) to the hash, and return to where you started, without using any segment of road twice or crossing a road you have passed through previously. (Bonus points if you manage to keep that up with the combined track log of several expeditions.)
That also implies, for example...
- you cannot go over the same footbridge on both the way to the hash and the way back
- you cannot go into any dead-end streets and back out of them again (even accidentally)
- you cannot go over bridges (and highway exits etc.) that put loops into your tracklog if it is drawn on a flat map
- you have to pass through the hashpoint (optionally stop to take pictures and such) and continue, but can't go back the same way
- when you get back, you have to approach your home from the opposite end of the road.
Tiny errors, such as might be recorded while standing at the hash taking pictures due to GPS position jitter, as well as the last few meters to your doorstep (but not your home road), are acceptable and do not invalidate the achievement. If you manage to go down opposite lanes of the same road which (at the accuracy of your GPS) are far enough apart to keep the tracklog from intersecting with itself, that is acceptable too. Note that if you do the expedition on your way to work or school (for example), the way back home afterwards counts as part of the journey - it has to be a (nearly) closed curve!
Unlike in the game, you may (have to) pause your ride at any point, of course. Taking minimal, linear side trips (such as walking into a store or restaurant on a longer expedition, or to get to a better spot for taking pictures) are acceptable if you explain them and don't take your vehicle with you on them (so that at least your vehicle's path doesn't intersect with itself). A "perfect" Tron-style expedition - one single ride without any overlapping track segments - is still the preferred way though.
Proving your success by posting the track log recorded by your GPS receiver is encouraged. For privacy, you may cut off the track in the vicinity of your home (but not the entire street, please). If you do not have a GPS, proving what route you took (or even remembering it with enough precision) might be difficult, but if you have to, a (sufficiently detailed and plausible) hand-drawn/google-earth-drawn route plot is probably acceptable.
Show your success with a ribbon.
| This user earned the Tron achievement
Everyone displaying the ribbon is listed in Category:Tron achievement.