The oft-quoted saying “all models are wrong, but some are useful” is a tounge-in-cheek way of saying that at some level, tools we use to predict how the world behaves will differ from reality in some measurable way. This goes well beyond the statistics classroom it is most often quoted in, too, and is especially apparent to anyone who has used a GPS mapping device of any sort. While we might think that our technological age can save us from the approximations of maps and models, there are a number of limitations with this technology that appear in sometimes surprising ways. [Kyle] has an interesting writeup about how maps can be wrong yet still be incredibly useful especially in the modern GPS-enabled world.

[Kyle] is coming to us with a background in outdoor travel, involving all kinds of activities like hiking and backcountry skiing. When dealing with GPS tracking under these conditions, often the user’s actual position will deviate from their recorded position by a significant margin. Obvious causes like a loss of GPS signal are one thing, but there are some other reasons for this behavior. GPS can be off by tens of meters, so the question then becomes whether or not mapping software should record these errors or attempt to guess where it thinks the most likely location is, based on available data like barometric pressure, existing trails, elevation profiles, and other data. Especially in areas where the elevation changes rapidly, these errors can compound quickly and provide some truly mystifying data. Where mapping software draws these distinctions is a matter of active debate in these communities, with some taking more approximate routes that make more sense while sacrificing the raw data, and others letting the GPS pins fall where they may.

For anyone who’s been confused by Strava or Garmin data at the end of a run, hike, or bike ride, this is a fairly informative explanation of why the GPS data might differ from the actual distance of any of these activities. [Kyle] also notes that unless you’re out with a measuring wheel (and perhaps even then) any method to determine a true distance like this will have some amount of approximation or error. The closest technological solution to a problem like this we’ve seen is this GPS receiver which claims centimeter-level precision using some unique tricks.

Through all the generations of computing devices from the era of the teleprinter to the present day, there’s one interface that’s remained universal. Even though its usefulness as an everyday port has decreased in the face of much faster competition, it’s fair to say that everything has a serial port on board somewhere. Even with that ubiquity though, there’s still some scope for variation.

Older ports and those that are still exposed via a D socket are in most case the so-called RS-232, a higher voltage port, while your microcontroller debug port will be so-called TTL (transistor-transistor logic), operating at logic level. That’s not quite always the case though, as [Terin Stock] found out with an older Garmin GPS unit.

Pleasingly for a three decade old device, given a fresh set of batteries it worked. The time was wrong, but after some fiddling and a Windows 98 machine spun up it applied a Garmin update from 1999 that fixed it. When hooked up to a Flipper Zero though, and after a mild panic about voltage levels, the serial port appeared to deliver garbage. There followed some investigation, with an interesting conclusion that TTL serial is usually the inverse of RS-232 serial, The Garmin had the RS-232 polarity with TTL levels, allowing it to work with many PC serial ports. A quick application of an inverter fixed the problem, and now Garmin and Flipper talk happily.