5 ms·

Gray code at the pediatrician's office

221 points by J3L2404 15y ago

ColinWright 15y ago
Previous discussions: http://news.ycombinator.com/item?id=667689 http://news.ycombinator.com/item?id=667689 http://news.ycombinator.com/item?id=899913 http://news.ycombinator.com/item?id=899913
- Corrado 15y ago
  OK, it may be an old question but why doesn't HN search for old URLs before allowing you to post? I missed this the first time around and am really glad that it got posted (and glad you found the dupes) but most reposts are bad. I think something like a URL check would be valuable.
  - ColinWright 15y ago
    There is a URL check, but it only finds exact matches, and only if the URL tested against is in memory. If it's old enough and hasn't been accessed recently, it's not found. I thought this was in jacquesm's FAQ, but it appears not to be: http://jacquesmattheij.com/The+Unofficial+HN+FAQ http://jacquesmattheij.com/The+Unofficial+HN+FAQ You might suggest it to him, although he's very busy.
- mjd 15y ago
  Also this: http://www.reddit.com/r/programming/comments/8ufl1/gray_code_at_the_pediatricians_office/ http://www.reddit.com/r/programming/comments/8ufl1/gray_code...
llimllib 15y ago
Here's another visualization of the Gray code: http://billmill.org/static/perm4.png http://billmill.org/static/perm4.png (it's from a few visualizations of permutations I did a while ago: http://billmill.org/permvis.html http://billmill.org/permvis.html )
fudged71 15y ago
This is incredibly interesting. Thank you!
orenmazor 15y ago
extremely fascinating, but what problem does this solve that a standard analog equivalent ruler/markings didn't?
- izak30 15y ago
  The optical machine doesn't have to count lines, it can read it's place on the bar from a small (2cm wide) part, rather than keeping an incrementer from the bottom or top.
  - orenmazor 15y ago
    I understand that. but whenever I'm at the doctor's they still have a graduated wall against which they put patients to get their height. I'm all for digitizing things, but is there any reason to replace this?
    - rch 15y ago
      Any medical data that can be recored in a mechanical fashion should be. The nurse writing things down is just a temporary artifact of the existing process.
    - uxp 15y ago
      In regard to digital measuring devices, they are much easier to recalibrate than say a strip of metal with graduated marks. This can lengthen it's lifetime of use, as well as speed installation and manufacturing time as neither has to be as precise as the analog versions. Another perceived benefit is that the indicator dial/display can be offset from the scale. I know I've seen some height gauges that partially cover the numbers that indicate their position. Digital solutions allow the measuring marks to be independent of how one takes the measurement.
      - tedunangst 15y ago
        Why would a ruler marked in binary not need to be as precise as a ruler marked in decimal? Changing the base of the numbers does little to affect how one attaches it to the wall.
anigbrowl 15y ago
Hmm. As a geek I like Gray code and think it has many useful applications, but this is not one of them: Iris stood against the post and the nurse adjusted the bracket to exactly the top of her head. Then she read off Iris's height from an attached display. How is this an advance on looking at a conventionally numbered ruler (with a similar bracket to touch the top of the head) and writing down the number? It's technological and presumably expensive, but it isn't delivering any discernible benefit that I can see. Measuring height via computer vision + Gray code would be very useful in security applications where you want to log biometric information for a large number of people efficiently (camera + abstract-looking wall design in an access corridor or at a security checkpoint), but if you're paying a human to take the measurement you might as well use a scale that's easily human-readable (ie at a glance). I hope the doctor's scale was at least using bluetooth or similar to automatically update the patient's digital record...but I wouldn't bet on it.
- TetOn 15y ago
  Presumably it's considered useful because there's a measurable error rate in the nurse a) reading -and/or- b) recording the observed data. Assuming this thing works properly more often, you've not only guaranteed you get the data entered properly, but it's more likely to be right.
  - falcolas 15y ago
    I imagine this is compounded by the subject matter being measured. A simple "click and lock the measurement" button would be invaluable when trying to measure the height of a squirming child. Simple, easy to read numbers that eliminate guesswork would seem to make a nurse's job much simpler (or allow them to utilize people who are not registered nurses to collect this data). There have been similar advances in scales, blood pressure cuffs, heart rate monitors, etc. All are readable using analog gauges, yet they progressed to digital devices.
  - cnvogel 15y ago
    What people here don't seem to realize is that a doctors' scale or measuring tapes are not used for precision measurements anyway. If the doctor sees the patient only every few months, individual variations (kids will grow, adults will gain (or, sometimes, hopefully) loose weight)) in body height or weight will exceed the precision you can get even out of the cheapest scale or measurement tape. And as for the purpose of the measurements: The doctor will use the values acquired from the tools to categorize patients in categories: E.g. a obese person has a higher risk of cardiac arrest, someone looking quite anorexic will have other problems with his blood chemistry... And here a few kilograms/centimeters don't influence the general statement at all.
Bdennyw 15y ago
When I looked at that pattern I though "Looks like one of Wolframs FSAs". And after reading the encoding algorithm, seems like it is. See http://demonstrations.wolfram.com/ElementaryCellularAutomatonRulesByGrayCode/ http://demonstrations.wolfram.com/ElementaryCellularAutomato...
clvv 15y ago
A partially related topic(maybe many of you already know): I was learning about minimizing logic expressions the other day, and I learned about the Karnaugh Map, which uses Gray code for its axes. You can read more about it here: http://en.wikipedia.org/wiki/Karnaugh_map http://en.wikipedia.org/wiki/Karnaugh_map
T-hawk 15y ago
Gray code was used as long ago as the Atari 2600 game system, designed in 1977. The system's clock for drawing out sprite graphics pixels counts in Gray code internally. Why? Because a binary adder could have too long a propagation delay. To increment 01111111 to 10000000 requires seven carry operations which would not always complete within a single clock cycle. (A modern ALU has tons of transistors to compute all those bits in parallel, but the Atari 2600 mass market game console did not have the budget for that many transistors.) Gray code was the solution. It always changes only one bit to increment a counter so the operation was guaranteed to complete quickly.
- DerekL 15y ago
  No, they didn't use Grey code for that, they used a "linear feedback shift register". A LFSR has lower propagation delay than a normal binary counter. The driving controllers did use Grey code.

221 points by J3L2404 15y ago

Previous discussions: http://news.ycombinator.com/item?id=667689 http://news.ycombinator.com/item?id=667689 http://news.ycombinator.com/item?id=899913 http://news.ycombinator.com/item?id=899913

Corrado 15y ago
OK, it may be an old question but why doesn't HN search for old URLs before allowing you to post? I missed this the first time around and am really glad that it got posted (and glad you found the dupes) but most reposts are bad. I think something like a URL check would be valuable.
- ColinWright 15y ago
  There is a URL check, but it only finds exact matches, and only if the URL tested against is in memory. If it's old enough and hasn't been accessed recently, it's not found. I thought this was in jacquesm's FAQ, but it appears not to be: http://jacquesmattheij.com/The+Unofficial+HN+FAQ http://jacquesmattheij.com/The+Unofficial+HN+FAQ You might suggest it to him, although he's very busy.
mjd 15y ago
Also this: http://www.reddit.com/r/programming/comments/8ufl1/gray_code_at_the_pediatricians_office/ http://www.reddit.com/r/programming/comments/8ufl1/gray_code...

llimllib 15y ago

Here's another visualization of the Gray code: http://billmill.org/static/perm4.png http://billmill.org/static/perm4.png (it's from a few visualizations of permutations I did a while ago: http://billmill.org/permvis.html http://billmill.org/permvis.html )

fudged71 15y ago

This is incredibly interesting. Thank you!

orenmazor 15y ago

extremely fascinating, but what problem does this solve that a standard analog equivalent ruler/markings didn't?

izak30 15y ago
The optical machine doesn't have to count lines, it can read it's place on the bar from a small (2cm wide) part, rather than keeping an incrementer from the bottom or top.
- orenmazor 15y ago
  I understand that. but whenever I'm at the doctor's they still have a graduated wall against which they put patients to get their height. I'm all for digitizing things, but is there any reason to replace this?
  - rch 15y ago
    Any medical data that can be recored in a mechanical fashion should be. The nurse writing things down is just a temporary artifact of the existing process.
  - uxp 15y ago
    In regard to digital measuring devices, they are much easier to recalibrate than say a strip of metal with graduated marks. This can lengthen it's lifetime of use, as well as speed installation and manufacturing time as neither has to be as precise as the analog versions. Another perceived benefit is that the indicator dial/display can be offset from the scale. I know I've seen some height gauges that partially cover the numbers that indicate their position. Digital solutions allow the measuring marks to be independent of how one takes the measurement.
    - tedunangst 15y ago
      Why would a ruler marked in binary not need to be as precise as a ruler marked in decimal? Changing the base of the numbers does little to affect how one attaches it to the wall.

anigbrowl 15y ago

Hmm. As a geek I like Gray code and think it has many useful applications, but this is not one of them: Iris stood against the post and the nurse adjusted the bracket to exactly the top of her head. Then she read off Iris's height from an attached display. How is this an advance on looking at a conventionally numbered ruler (with a similar bracket to touch the top of the head) and writing down the number? It's technological and presumably expensive, but it isn't delivering any discernible benefit that I can see. Measuring height via computer vision + Gray code would be very useful in security applications where you want to log biometric information for a large number of people efficiently (camera + abstract-looking wall design in an access corridor or at a security checkpoint), but if you're paying a human to take the measurement you might as well use a scale that's easily human-readable (ie at a glance). I hope the doctor's scale was at least using bluetooth or similar to automatically update the patient's digital record...but I wouldn't bet on it.

TetOn 15y ago
Presumably it's considered useful because there's a measurable error rate in the nurse a) reading -and/or- b) recording the observed data. Assuming this thing works properly more often, you've not only guaranteed you get the data entered properly, but it's more likely to be right.
- falcolas 15y ago
  I imagine this is compounded by the subject matter being measured. A simple "click and lock the measurement" button would be invaluable when trying to measure the height of a squirming child. Simple, easy to read numbers that eliminate guesswork would seem to make a nurse's job much simpler (or allow them to utilize people who are not registered nurses to collect this data). There have been similar advances in scales, blood pressure cuffs, heart rate monitors, etc. All are readable using analog gauges, yet they progressed to digital devices.
- cnvogel 15y ago
  What people here don't seem to realize is that a doctors' scale or measuring tapes are not used for precision measurements anyway. If the doctor sees the patient only every few months, individual variations (kids will grow, adults will gain (or, sometimes, hopefully) loose weight)) in body height or weight will exceed the precision you can get even out of the cheapest scale or measurement tape. And as for the purpose of the measurements: The doctor will use the values acquired from the tools to categorize patients in categories: E.g. a obese person has a higher risk of cardiac arrest, someone looking quite anorexic will have other problems with his blood chemistry... And here a few kilograms/centimeters don't influence the general statement at all.

Bdennyw 15y ago

When I looked at that pattern I though "Looks like one of Wolframs FSAs". And after reading the encoding algorithm, seems like it is. See http://demonstrations.wolfram.com/ElementaryCellularAutomatonRulesByGrayCode/ http://demonstrations.wolfram.com/ElementaryCellularAutomato...

clvv 15y ago

A partially related topic(maybe many of you already know): I was learning about minimizing logic expressions the other day, and I learned about the Karnaugh Map, which uses Gray code for its axes. You can read more about it here: http://en.wikipedia.org/wiki/Karnaugh_map http://en.wikipedia.org/wiki/Karnaugh_map

T-hawk 15y ago

Gray code was used as long ago as the Atari 2600 game system, designed in 1977. The system's clock for drawing out sprite graphics pixels counts in Gray code internally. Why? Because a binary adder could have too long a propagation delay. To increment 01111111 to 10000000 requires seven carry operations which would not always complete within a single clock cycle. (A modern ALU has tons of transistors to compute all those bits in parallel, but the Atari 2600 mass market game console did not have the budget for that many transistors.) Gray code was the solution. It always changes only one bit to increment a counter so the operation was guaranteed to complete quickly.

DerekL 15y ago
No, they didn't use Grey code for that, they used a "linear feedback shift register". A LFSR has lower propagation delay than a normal binary counter. The driving controllers did use Grey code.