Quoted message said:Sneaky scales fudge weights deliberately.
I suspect that many modern, microprocessor -controlled bathroom scales
have programmed in hysteresis to increase user confidence in the
scale's accuracy. The scale remembers fresh measurements, say 166.2#,
and if it next measures same weight +/- a little (within a short time),
say 166.8#, then the scale decides to report the *original* measurement
166.2#. Neat. Sneaky. User believes the scale is highly repeatable.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.I tried 6 models (2 or 3 brands) at a retail store display and find
this "feature" common.Is it important? Maybe yes in the following scenario -- in some sports
like wrestling, boxing, judo, you have multiple competitors weighing in
at the same time, same scale, with possibly very similar weight. Some
competitors are concerned with as little as 0.25#. In this case it
seems one competitor could inherit the weight measurement of the person
in front of him.In a perfect world, competition weigh-in equipment should be
certified/calibrated. But since the bathroom scale appears so
repeatable, some competitions now use modern, microprocessor
-controlled bathroom scales.Somebody's going to say... "you shouldn't do that". Right, I agree.
But (a) it's happening, because (b) this hysteresis (memory)phenomenon
isn't widely known, I suspect.Anyone care to confirm? Contradict? Repeat the experiment on their
own scale? Comment? In my experiment I didn't bother to determine
what weight difference resets the memory -- 1#? 1.5#?Regards,
John Ruckstuhl
Having spent some time in the weiging industry, i can assure you that
the cheap portable bathroom scales that you buy are neither:
a. repeatable
b. accurate
c. linear
In fact, most will become more innacurate in the most common weight
ranges.
In AU, a cheap set is $20, a good repeatable set is $400. The
expensive scale can be recalibrate and remains linear. Should it not
be linear a multi-point cal can be done. The cheap set can only be
thrown.
Most cheap sets are innacurate of the shelf as they are made in china
and fail to take into account local gravitational constants