Re: bathroom scale hysteresis

"Robert Baer" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

[email hidden] wrote:

Quoted message said:

Bathroom scales have historically been rather (to be polite) inaccurate.
Notice in a grocery that the scales are all spring scales (ie:
inexpensive) and are marked "NOT FOR TRADE" or "NOT LEGAL FOR TRADE".
They all read *approximate* values, and if not calibrated, can be off by
20 percent of full scale (either way) for starters.
If you want more reliable or accurate readings, use a balance type of
scale: Toledo comes to mind, Cenco comes to mind; there are others.

I've noticed with balance scales that the weight shifts by several pounds
depending upon where you stand on it ... I assume you're supposed
to stand more or less in the center, an inch one way or another can
make a difference of a pound or two (important if you're doing a
sport with weight divisions).

-JS2

"I've noticed with balance scales that the weight shifts by several
pounds
depending upon where you stand on it ... I assume you're supposed
to stand more or less in the center, an inch one way or another can
make a difference of a pound or two (important if you're doing a
sport with weight divisions)."

This would be the incentive to repeat the last reading. This would make
the electronic scale seem more dependable, stop customers from worrying
about water weight gains and losses. It would take a very small amount
of digital memory and programing. I am sure there is even memory for
two or three "normal weights". There is probably a mass produced chip
that includes this program and you will need to find one with a
different chip to change the repeat. I bet you even paid extra for the
"added accuracy"!

JS2 said:

"Robert Baer" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

[email hidden] wrote:

Quoted message said:

Bathroom scales have historically been rather (to be polite) inaccurate.
Notice in a grocery that the scales are all spring scales (ie:
inexpensive) and are marked "NOT FOR TRADE" or "NOT LEGAL FOR TRADE".
They all read *approximate* values, and if not calibrated, can be off by
20 percent of full scale (either way) for starters.
If you want more reliable or accurate readings, use a balance type of
scale: Toledo comes to mind, Cenco comes to mind; there are others.

I've noticed with balance scales that the weight shifts by several pounds
depending upon where you stand on it ... I assume you're supposed
to stand more or less in the center, an inch one way or another can
make a difference of a pound or two (important if you're doing a
sport with weight divisions).

Not only have I never heard of such a thing, I've seen the workings
of scales that go to great lengths to avoid just that. If your scale
shows different weights when the object is on different places on
the platform, then you have been robbed.

Cheers!
Rich

Quantum Mirror said:

"I've noticed with balance scales that the weight shifts by several
pounds
depending upon where you stand on it ... I assume you're supposed
to stand more or less in the center, an inch one way or another can
make a difference of a pound or two (important if you're doing a
sport with weight divisions)."

This would be the incentive to repeat the last reading. This would make
the electronic scale seem more dependable, stop customers from worrying
about water weight gains and losses. It would take a very small amount
of digital memory and programing. I am sure there is even memory for
two or three "normal weights". There is probably a mass produced chip
that includes this program and you will need to find one with a
different chip to change the repeat. I bet you even paid extra for the
"added accuracy"!

Now this is just plain silly. Who in their right mind would go to
such great lengths, just to produce a reading that isn't even what
the weight on the platform is?

The phenomenon that the OP, John Ruckstuhl, mentioned:
"On such a scale, I weigh myself multiple times and get the same reading
(to the 0.2#) each time. 166.2#, 166.2#, 166.2#, 166.2#, ... Then I
weigh something different (myself holding a load), to reset the memory.
Then I weigh myself again... Now, get something like 166.8#, 166.8#, 166.8#,
166.8#, ... very solid again, but 0.6# different from 1st series of
measurements."

Is from hysteresis. He steps on the transducer, it's been sitting all
day stabilizing, so it reads low. He steps on the scale holding weights,
It shows his 166.2 + the weight + some unknown error. He steps off
the scale, and it springs back to something greater than zero; the
scale waits until it's done bouncing, re-zeros itself, and now when
he steps back on it's biased high. The effect would probably be even
worse if he just stayed standing there and set the weight down.

The point being that the sensor takes a "set." And, probably not
so much these days with little strain gauges, but with mechanical
scales, there's sticktion to deal with.

Cheers!
Rich

"Rich Grise" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

JS2 said:

"Robert Baer" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

[email hidden] wrote:

Quoted message said:

Bathroom scales have historically been rather (to be polite)
inaccurate.
Notice in a grocery that the scales are all spring scales (ie:
inexpensive) and are marked "NOT FOR TRADE" or "NOT LEGAL FOR TRADE".
They all read *approximate* values, and if not calibrated, can be off
by
20 percent of full scale (either way) for starters.
If you want more reliable or accurate readings, use a balance type of
scale: Toledo comes to mind, Cenco comes to mind; there are others.

I've noticed with balance scales that the weight shifts by several pounds
depending upon where you stand on it ... I assume you're supposed
to stand more or less in the center, an inch one way or another can
make a difference of a pound or two (important if you're doing a
sport with weight divisions).

Not only have I never heard of such a thing, I've seen the workings
of scales that go to great lengths to avoid just that. If your scale
shows different weights when the object is on different places on
the platform, then you have been robbed.

I've seen it on doctor's scales, and the typical scale (lever arm with
weights) used in most gyms (don't have any kind of scale at home),
and hence in wrestling and judo competitions. Maybe they're just
old scales so some internal mechanism is worn out, but it seems to
be very common. Not an issue if you're looking to measure your
weight accurately (just stand at the center), but something that can
be used to your advantage (or disadvantage) if you're making
weight division and even a half pound makes or breaks you. My
thought was that if the scale isn't designed properly, it might change
the action point on the lever arm (even .5% change is good for a
pound if you're about 200 lbs).

-JS2

Rich Grise said:

JS2 said:

"Robert Baer" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

[email hidden] wrote:

Quoted message said:

Bathroom scales have historically been rather (to be polite) inaccurate.
Notice in a grocery that the scales are all spring scales (ie:
inexpensive) and are marked "NOT FOR TRADE" or "NOT LEGAL FOR TRADE".
They all read *approximate* values, and if not calibrated, can be off by
20 percent of full scale (either way) for starters.
If you want more reliable or accurate readings, use a balance type of
scale: Toledo comes to mind, Cenco comes to mind; there are others.

I've noticed with balance scales that the weight shifts by several pounds
depending upon where you stand on it ... I assume you're supposed
to stand more or less in the center, an inch one way or another can
make a difference of a pound or two (important if you're doing a
sport with weight divisions).

Not only have I never heard of such a thing, I've seen the workings
of scales that go to great lengths to avoid just that. If your scale
shows different weights when the object is on different places on
the platform, then you have been robbed.

Cheers!
Rich

This would not explain my experience, just picking up a little extra
weight each time and getting back on the scale. It just would not move
until about 5 pounds total had been added. Only explanation I have is
that is it 'faking' the accuracy; and doing it quite intentionally.

That's why is on my list of projects for re-engineering. Maybe Mavin's
voice "You standing on my like that is just so Depressing!"

--
Luhan Monat: luhanis(at)yahoo(dot)com
http://members.cox.net/berniekm
"Any sufficiently advanced magick is
indistinguishable from technology."

"JS2" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

"Robert Baer" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

[email hidden] wrote:

Quoted message said:

Bathroom scales have historically been rather (to be polite)
inaccurate.
Notice in a grocery that the scales are all spring scales (ie:
inexpensive) and are marked "NOT FOR TRADE" or "NOT LEGAL FOR TRADE".
They all read *approximate* values, and if not calibrated, can be off
by 20 percent of full scale (either way) for starters.
If you want more reliable or accurate readings, use a balance type of
scale: Toledo comes to mind, Cenco comes to mind; there are others.

I've noticed with balance scales that the weight shifts by several pounds
depending upon where you stand on it ... I assume you're supposed
to stand more or less in the center, an inch one way or another can
make a difference of a pound or two (important if you're doing a
sport with weight divisions).

-JS2

A properly designed and calibrated scale should not exhibit this behavior.
Calibrations should be performed according to NIST Handbook 44, which
includes a shift test, a return to zero (testing mechanical hysteresis), an
increasing load test and others depending on the type of scale.

Also, ISO 17025 for calibration labs require all as found readings to be
measured and reported before any adjustments to calibration are made. As
left readings are also recorded. Acceptance tolerances and maintainance
tolerances are specified in Handbook 44 and vary by Class specifications.
Most legal-for-trade requirements defer to Handbook 44.

Luhan Monat said:

Rich Grise said:

JS2 said:

"Robert Baer" <[email hidden]> wrote in message
>[email hidden] wrote:

> Bathroom scales have historically been rather (to be polite) inaccurate.
> Notice in a grocery that the scales are all spring scales (ie:
>inexpensive) and are marked "NOT FOR TRADE" or "NOT LEGAL FOR TRADE".
> They all read *approximate* values, and if not calibrated, can be off by
>20 percent of full scale (either way) for starters.
> If you want more reliable or accurate readings, use a balance type of
>scale: Toledo comes to mind, Cenco comes to mind; there are others.

I've noticed with balance scales that the weight shifts by several pounds
depending upon where you stand on it ... I assume you're supposed
to stand more or less in the center, an inch one way or another can
make a difference of a pound or two (important if you're doing a
sport with weight divisions).

Not only have I never heard of such a thing, I've seen the workings
of scales that go to great lengths to avoid just that. If your scale
shows different weights when the object is on different places on
the platform, then you have been robbed.

This would not explain my experience, just picking up a little extra
weight each time and getting back on the scale. It just would not move
until about 5 pounds total had been added. Only explanation I have is
that is it 'faking' the accuracy; and doing it quite intentionally.

That's why is on my list of projects for re-engineering. Maybe Mavin's
voice "You standing on my like that is just so Depressing!"

I've answered this in a different branch - the sensor has a certain
amount of hysteresis, but also excellent "repeatability" as long as
you haven't moved the sensor's threshold in between, which is what
John says is happening. The sensor takes a "set", or something very
much like that. But I guess I'd have trouble blaming sticktion when
they're using strain gauges - but anything, to measure how hard it
is being stressed or strained, has to have some kind of change take
place, or there wouldn't be any signal. Generally, that's movement
of some kind. So, if it's something that flexes, it simply doesn't unflex
back to _precisely_ the same position, for any number of reasons. At least
not right away. Probably after awhile, yes. So when he first gets on, the
sensor has been relaxing all night, so has no "set." He steps on the scale
first time, and puts whatever "set" that 166.2 puts on it. Then, when
he steps off and on, The force on it is the same, so it doesn't add any
"set", and since the thing has good repeatabilty, it reads the same. Then,
he steps on it with weights on, and it reads, say, 191.2. (It would be
very interesting to see this number, if the weights are calibrated). This
increases the "set" to S(191.2). Now, he puts 166.2 on it, but it doesn't
have enough force to even _reach_ the higher "set," so effectively zero
has backed away by 0.6, and it reads 166.8.

Nothin' to it! ;-)

Cheers!
Rich

Rich Grise said:

Luhan Monat said:

Rich Grise said:

On Sat, 28 May 2005 08:38:23 -0600, JS2 wrote:

>"Robert Baer" <[email hidden]> wrote in message
>
>>[email hidden] wrote:
>
>> Bathroom scales have historically been rather (to be polite) inaccurate.
>> Notice in a grocery that the scales are all spring scales (ie:
>>inexpensive) and are marked "NOT FOR TRADE" or "NOT LEGAL FOR TRADE".
>> They all read *approximate* values, and if not calibrated, can be off by
>>20 percent of full scale (either way) for starters.
>> If you want more reliable or accurate readings, use a balance type of
>>scale: Toledo comes to mind, Cenco comes to mind; there are others.
>
>I've noticed with balance scales that the weight shifts by several pounds
>depending upon where you stand on it ... I assume you're supposed
>to stand more or less in the center, an inch one way or another can
>make a difference of a pound or two (important if you're doing a
>sport with weight divisions).

Not only have I never heard of such a thing, I've seen the workings
of scales that go to great lengths to avoid just that. If your scale
shows different weights when the object is on different places on
the platform, then you have been robbed.

This would not explain my experience, just picking up a little extra
weight each time and getting back on the scale. It just would not move
until about 5 pounds total had been added. Only explanation I have is
that is it 'faking' the accuracy; and doing it quite intentionally.

That's why is on my list of projects for re-engineering. Maybe Mavin's
voice "You standing on my like that is just so Depressing!"

I've answered this in a different branch - the sensor has a certain
amount of hysteresis, but also excellent "repeatability" as long as
you haven't moved the sensor's threshold in between, which is what
John says is happening. The sensor takes a "set", or something very
much like that. But I guess I'd have trouble blaming sticktion when
they're using strain gauges - but anything, to measure how hard it
is being stressed or strained, has to have some kind of change take
place, or there wouldn't be any signal. Generally, that's movement
of some kind. So, if it's something that flexes, it simply doesn't unflex
back to _precisely_ the same position, for any number of reasons. At least
not right away. Probably after awhile, yes. So when he first gets on, the
sensor has been relaxing all night, so has no "set." He steps on the scale
first time, and puts whatever "set" that 166.2 puts on it. Then, when
he steps off and on, The force on it is the same, so it doesn't add any
"set", and since the thing has good repeatabilty, it reads the same. Then,
he steps on it with weights on, and it reads, say, 191.2. (It would be
very interesting to see this number, if the weights are calibrated). This
increases the "set" to S(191.2). Now, he puts 166.2 on it, but it doesn't
have enough force to even _reach_ the higher "set," so effectively zero
has backed away by 0.6, and it reads 166.8.

Nothin' to it! ;-)

Cheers!
Rich

Sorry, something is getting missed here. I kept picking up an extra
pound of stuff each time and then getting back on the scale. So it had
some chance to re-zero. But all it did was report exactly the same
weight each time. When the accumulated extra weight was about 5 pounds,
then, and only then, did it jump to a new weight. Then again, it
claimed that to be the real weight as a dropped off a pound at a time
getting on and off the scale.

The software in the scale was obviously fudging the numbers to produce a
false sense of accuracy.

--
Luhan Monat: luhanis(at)yahoo(dot)com
http://members.cox.net/berniekm
"Any sufficiently advanced magick is
indistinguishable from technology."

On Sat, 28 May 2005 15:17:48 -0700, Luhan Monat <[email hidden]> wroth:

Quoted message said:

Sorry, something is getting missed here. I kept picking up an extra
pound of stuff each time and then getting back on the scale. So it had
some chance to re-zero. But all it did was report exactly the same
weight each time. When the accumulated extra weight was about 5 pounds,
then, and only then, did it jump to a new weight. Then again, it
claimed that to be the real weight as a dropped off a pound at a time
getting on and off the scale.

The software in the scale was obviously fudging the numbers to produce a
false sense of accuracy.

I'd be willing to bet that there is a sticker on the scale or a note in
the owners manual with a phrase like "... not legal for trade".

You bought a freakin' bathroom scale fer cripe's sake, not a NIST
certified research instrument. Get over it.

Jim

For about $180 you can get a freon charging scale with 400 lb range and
accurate and reproducible to a fraction of an ounce. I guarantee there
is no funny stuff like you are seeing in the firmware :-). I forget the
brand we got last year at work but it has those specs.

--
Regards,
Carl Ijames carl.ijames at verizon.net

Rich Grise said:

JS2 said:

I've noticed with balance scales that the weight shifts by several pounds
depending upon where you stand on it ... I assume you're supposed
to stand more or less in the center, an inch one way or another can
make a difference of a pound or two (important if you're doing a
sport with weight divisions).

Not only have I never heard of such a thing, I've seen the workings
of scales that go to great lengths to avoid just that. If your scale
shows different weights when the object is on different places on
the platform, then you have been robbed.

I think it is quite common. Mine does the same thing. What I do is
move about to get the maximum, then the minimum, then split the
difference (typically about 5 kilos!).

--

John Devereux

Luhan Monat said:

Rich Grise wrote:

Quoted message said:

Quoted message said:

Nothin' to it! ;-)

Sorry, something is getting missed here. I kept picking up an extra
pound of stuff each time and then getting back on the scale. So it had
some chance to re-zero. But all it did was report exactly the same
weight each time. When the accumulated extra weight was about 5 pounds,
then, and only then, did it jump to a new weight. Then again, it
claimed that to be the real weight as a dropped off a pound at a time
getting on and off the scale.

Then your scale is lying to you. It actually has a resolution of 5 lbs,
but since the designers thought that wouldn't sell well, they just
make up some random interval, or maybe interpolate based on the time
of day or barometric pressure or something.

Quoted message said:

The software in the scale was obviously fudging the numbers to produce a
false sense of accuracy.

Yes. Obviously. :-)

Did you get it for $5.00 at an auction? ;-)

Cheers!
Rich

GaryG said:

I think you just got a bad scale. My 4-year old Tanita does not have
that problem at all. I can step on and off, and always get the same
reading (or, within the 0.2 lb resolution). If I step off, drink an 8
oz glass of water, and step back on, it shows that I've gained 1/2 lb.
If I weigh myself before and after a [censored], it shows (appropriately)
1.5-2 lbs lost.

What a load of [censored]! ;-D
--
The Pig Bladder from Uranus, still waiting for that hot babe to ask
what my favorite planet is.

In article <[email hidden]>,

JS2 said:

I've noticed with balance scales that the weight shifts by several pounds
depending upon where you stand on it ... I assume you're supposed
to stand more or less in the center, an inch one way or another can
make a difference of a pound or two (important if you're doing a
sport with weight divisions).

A balance scale at a gym I used to frequent had about a 5 lb
difference at the 200 lbs mark, depending on whether you moved the big
weight to the 200 lb notch, or moved it to the 150 lb notch and the
small weight to the 50 lb mark.

Seth
--
Don't ever masturbate after getting capsaicin on your hands. -- Patrick Arnold