I'm building an application that runs on a tablet connected to an exercise machine (a rowing machine)> The tablet is running a video of the instructor, and overlaying the video is the performance of the rower - current pace, number of meters completed, stuff like that.

Some of these performance stats update very quickly - the datastream is 100Hz. It doesn't make sense to update the numbers that often. They'd be a blur. On the other hand, updating the progress every 2 seconds is frustrating. As a rower I am spending all my attention "waiting" for another update when I'd be happier if I was "free" to focus on other things.

I looked around for some literature about perception on updating numbers and I couldn't find any thing relevant. Anyone have a pointer for me? How often should the numbers update on the tablet?

  • Can you get information from the machine like stroke or revolution starts and ends? If so, it might be worth using those to set you update frequency - i.e. update once every stroke or once every revolution - That way the user is seeing exactly what changed in the most recent stroke/revolution and the faster they work the faster the updates will come. Jul 27 '18 at 10:39

Why not let the user decided?

If it's technically possible you could provide a slider (I'd do a sketch if I could on this laptop of a turtle at one end and a hare at the other) for the user to pick how frequently the data updates on their tablet. Some rowers will want to see it as quick as possible so they can adjust their rhythm etc and other rowers will just want it as an indication that they are on the right track.

  • 1
    I like the idea of presenting the stats visualy and not only in numbers.
    – BrunoH
    Jul 27 '18 at 11:49

My initial thought was "what about a blink of an eye?" which would be roughly 1/3 of a second.

However since you want a "smooth graph" I guess based on your answer to @sclarke

"I like the idea of presenting the stats visualy and not only in numbers"

I instead thought well: movies have 24 fps which would ofc be 1/24 of a second.

See reference: https://en.wikipedia.org/wiki/24p

But I am thinking that you probably wouldn't look at the stats all the time either.

So if you take the average reaction time instead (roughly 250) that's just less under the blinking time and updating about 4 times a second would probably be enough. Sure you would have some "stutter updates" but in a graph for example if you get for updates a second I believe this would be acceptable by most people.

See reference: http://www.odec.ca/projects/2011/leewa2/results.html


But I do want to point up that @sclarke's answer is probably the best. Let the user decide.

Sure if you want "pure realtime updates" you should go for each "tick".

To play the devils advocate: What if people feel like they "have to workout faster" because nothing is happening on the screen for a half second or so. If there's a fixed update rate I don't think people care as much when it actually updating. I have no facts to back this theory up though.

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