If the scale has automatic zero and
most do then it will keep making internal
adjustments to correct any drift while the display shows zero and this
can lead to the first amount of weight not being counted if it was not
enough to get the scale off the mark. This may have been the reason
that tests marked *3 were slightly out. You can avoid the auto
causing errors by ensuring that the first weight added is a couple of
grams or so.
(how to get around a problem)
Thanks to MB
who has brought my
attention to this reference http://www.rightonscales.com/web/learnmore.htm#autozero
to the auto zero function causing the lower reading. ....and to
this reference ahttp://www.jscale.com/support.html
about halfway down the page. Which explains that " Adding light loads
"dribbling" can cause display problems. " .
The problem that I think my old scales have a correction that is applied by
the scale no mater what the display shows.
Seems to apply to older digital scales.
The heart of a digital scale is the
load-cell which converts the load on the platform into a signal
that is processed by the internal computer and the result is shown on the
display. The load-cell, the platform support mechanism and associated
circuitry has some problems that can be overcome by the software in the
One problem is drift. If drift is
not "solved" in some manner it could lead to customer dissatisfaction.
Uncompensated drift causes the display slowly change when the scale is
just sitting there with or without weight on it.
How a manufacturer could
handle the "problem" of drift.
By careful design it may be possible to eliminate drift to the extent
that it is not apparent on the display in the time usually necessary to
complete a weighing operation or the scale turns off. In this case the
drift is less than the
smallest display unit. If the display increments in larger, say 2g
is less critical. If the range of weight that the scale has to handle
is less, drift is less. If the scale turns itself off quickly there
is less time for drift to occur.
If the cost and complexity is too great to fix drift it could be just
left as a visible problem. In this case occasionally the display may
slowly drift in one direction.
You could redefine the "problem" from one that affects accuracy to a
"problem" that causes customer feedback. The new "problem" then is to
eliminate the customer feedback. This could be done by cloaking the
drift. Drift will occur slowly so the computer is programmed to watch
for any slow change in weight and to presume it is drift and to apply a
correction. Basically the computer notes that the weight has slowly
risen by say 1g and concludes it is drift and subtracts 1g off the
weight. The display does not change and the customer is unaware of the
correction. You can see now that slowly adding weight to the scale has
brought this "feature" of the scale into play and impacted on the
Perhaps all scales make drift corrections and the ones that give
incorrect values in the test above apply the correction too quickly
fail to undo the correction when it turns out to not be needed.
What does this all mean
Do the test on your
scales rejoice if you do not have the
problem. If you do then:-
However much you are weighing out it is perhaps only
10g will be added slowly and now you know not to sprinkle in small
amounts you should only be over by no more than a gram regardless
of the amount you are weighing. The "problem" makes "weighing
amounts say up to 20g difficult to do accurately but a 1g division
scale is not meant for such work. I "weighed out"
gram lots of yeast on my old scales and the results were 11.77, 11.94,
11.07, 10.65. the
more careful i.e. the slower I was the more the problem affected the