3 ms·

The digital speedometer on my vehicle is surrounded by an "analog" speedometer. I'm not sure why anyone would need it to determine whether they are accelerating

The digital speedometer on my vehicle is surrounded by an "analog" speedometer. I'm not sure why anyone would need it to determine whether they are accelerating or decelerating, but it's there.

cvoss 3y ago
If you want to maintain a particular speed, you need to know not only your current speed but also your acceleration. Otherwise you are frequently going to be slipping pretty far off your target before you notice. High latency control loops like that are an impediment to precision. If you are accelerating at 1 mph per second, it can take up to an entire second for the digital display to indicate that you are accelerating at all, and, even then, you still don't know how fast you are accelerating. The resolution just isn't good enough.
- jjk166 3y ago
  Humans can detect accelerations as low as .25 mph/s so while you might not know exactly what your acceleration rate is, you definitely would be aware that you are accelerating and whether your efforts to compensate are increasing or decreasing it. And these very low acceleration rates take a very long time to significantly alter your speed. On an analogue dial you probably wouldn't even notice the movement. In practice, maintaining speed in a vehicle is pretty darn simple.
  - lmm 3y ago
    > Humans can detect accelerations as low as .25 mph/s Maybe under ideal conditions. Not while driving. And below .25 is still enough to have you drift off speed. > you definitely would be aware that you are accelerating and whether your efforts to compensate are increasing or decreasing it. It is by no means definite. It's very easy to drift off the correct speed when e.g. the slope of the road changes, even if you're trying not to.
    - jjk166 3y ago
      With what level of precision are you trying to maintain constant speed? At .25 mph/s it takes 4 seconds to have a 1 mph change in speed. At highway speeds the change in your position from where you'd expect to be at perfectly constant velocity would be 0.8%, or about 3 feet off. That's nothing compared to the variability of your speedometer, which is only accurate to about +/- 10%. If you're a blue angel trying to fly in close formation at hundreds of miles per hour, yeah that's not good enough, but for a normal person driving on a road it is trivially simple to keep your speed within the margin of error of your speedometer.
  - Turskarama 3y ago
    You might be able to detect an acceleration, but I bet you can't accurate gauge how fast that acceleration is.
    - jjk166 3y ago
      But why do you need to gauge rate of acceleration? If you're trying to maintain constant speed, you want an absence of acceleration.
jdietrich 3y ago
It's easier to eyeball an angle at a glance than to read a number. Some digital speedos subtly change color as you approach and exceed the speed limit, which is a particularly elegant affordance.

The digital speedometer on my vehicle is surrounded by an "analog" speedometer. I'm not sure why anyone would need it to determine whether they are accelerating or decelerating, but it's there.

cvoss 3y ago

If you want to maintain a particular speed, you need to know not only your current speed but also your acceleration. Otherwise you are frequently going to be slipping pretty far off your target before you notice. High latency control loops like that are an impediment to precision. If you are accelerating at 1 mph per second, it can take up to an entire second for the digital display to indicate that you are accelerating at all, and, even then, you still don't know how fast you are accelerating. The resolution just isn't good enough.

jjk166 3y ago
Humans can detect accelerations as low as .25 mph/s so while you might not know exactly what your acceleration rate is, you definitely would be aware that you are accelerating and whether your efforts to compensate are increasing or decreasing it. And these very low acceleration rates take a very long time to significantly alter your speed. On an analogue dial you probably wouldn't even notice the movement. In practice, maintaining speed in a vehicle is pretty darn simple.
- lmm 3y ago
  > Humans can detect accelerations as low as .25 mph/s Maybe under ideal conditions. Not while driving. And below .25 is still enough to have you drift off speed. > you definitely would be aware that you are accelerating and whether your efforts to compensate are increasing or decreasing it. It is by no means definite. It's very easy to drift off the correct speed when e.g. the slope of the road changes, even if you're trying not to.
  - jjk166 3y ago
    With what level of precision are you trying to maintain constant speed? At .25 mph/s it takes 4 seconds to have a 1 mph change in speed. At highway speeds the change in your position from where you'd expect to be at perfectly constant velocity would be 0.8%, or about 3 feet off. That's nothing compared to the variability of your speedometer, which is only accurate to about +/- 10%. If you're a blue angel trying to fly in close formation at hundreds of miles per hour, yeah that's not good enough, but for a normal person driving on a road it is trivially simple to keep your speed within the margin of error of your speedometer.
- Turskarama 3y ago
  You might be able to detect an acceleration, but I bet you can't accurate gauge how fast that acceleration is.
  - jjk166 3y ago
    But why do you need to gauge rate of acceleration? If you're trying to maintain constant speed, you want an absence of acceleration.

jdietrich 3y ago

It's easier to eyeball an angle at a glance than to read a number. Some digital speedos subtly change color as you approach and exceed the speed limit, which is a particularly elegant affordance.