Verifying a Weighing Scale by Using a Bottled Water-Simple Trick To Avoid Being Cheated

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bottled-water

As a common consumer, I usually go to market or groceries every week,  if not every day.  In the market or groceries where meat and vegetable are sold, a weighing scale (either a digital or analog) is used before a price is set for a certain product you buy.

The basis of their pricing is the weighing scale. They cannot set the purchased price without this (unless they just sell by the sack or by cans) so it is always visible in the area.  Nowadays, more advance scales are programmed where prices are already computed basing it on its weight.

In these days where technology is always used as a tool to improve our lives, sometimes it is also used or being used to give unsatisfactory results.

I have written this post as a guide whenever we purchase something where weighing is related, to provide some tips on how to avoid being cheated in the market area just by using what we already have and always carry with us, a bottled water.

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A digital weighing scale where the price is displayed automatically with weight.

We are Not Aware!

Most of us when  using the weighing scale does not think if the weighing scale used is accurate or not, simply because we are not aware regarding the accuracy of the scale or maybe we trust the weighing scale (and the seller) or maybe the expected amount is already acceptable to us. We do not even ask if the weighing scale they use is calibrated or not. (But how do we know it is calibrated?

A calibrated weighing scale should have a calibration sticker and a calibration seal placed visibly on its body. See below photo. This will indicate the calibration date and calibration due date of the weighing scale.

sample calibration sticker and calibration seal

please visit this link to know more about a calibrated instruments).

But what do you feel if you buy a kilo of meat regularly then suddenly when you check it at home or to other more accurate and trusted weighing scale it is only 900 grams (0.9 kilos)? 100 grams is already deducted from you but you had paid  exact amount for a 1 kilo of meat (you have been cheated!) .

Of course, it will make you mad  and next time, you will not go back to that seller.  It could be his fault or the weighing scales fault, but the true reason we do not know.

Need to be Aware!

I will share  with you in this topic on how we can avoid this kind of problem in case you encounter or if it happens that you buy some meat in the market and you are not sure whether the scale is displaying an acceptable reading.

Acceptable because there are no 100% accurate reading, there is always an inaccuracy or we call it uncertainty.  But if this uncertainty is very small, then it is not a big problem to us. We need to be aware in this kind of situation in order for us to be protected and not to be cheated.

The Standard Verification

First, I just want to show the standard way of checking the accuracy of a weighing scale (without the technicals). In order to check the accuracy or if the reading of the scale is acceptable, we need a standard weight ( or mass), this standard weight is certified from a calibration laboratory.

The reading is compared between the weighing scale and the standard weight, this is called Calibration and a calibration technician is the one handling this.  If it is a 1kilo Standard Weight, when you put it on a weighing scale, it should also display 1kilo. In this way, if they have the same reading, we can say that the weighing scale is accurate.

But usually, in calibration, a set of masses/ weights are used to verify the full range of the weighing scale. But for the reason of verification, one standard weight is fine.

Visit this link to see how a  digital weighing scale is calibrated in a laboratory.

weighing-scale-with-standard-mass
Weighing scale with a 1 Kg Standard Weight
1 Kg Standard Weight

In connection for this,  since we do not carry a standard weight    (which is not practical, this is expensive and heavy) if we are going to the market, one thing that I observe that can be used in replacement for the standard mass is a bottled water. Yes, a bottled water!

Why?

In the advancement of technology, bottled water is already affordable to everybody. Today, most people are always carrying a bottled water with them wherever they go.

Since  a bottled water is manufactured in a finite  or with an exact container and a volume, it has also an exact weight.

So it is also wise to use this as a check standard during weighing in replacement for a standard weight. We do not need a super accurate standard like the standard weights; we just want to know if the expected reading being displayed is correct and acceptable.

How?

Just a simple conversion:

0.5 Liter or 500 ml =  0.5 Kilogram  or 500 grams

0.6 Liter or 600 ml =  0.6 Kilogram  or 600 grams

1 Liter or 1000 ml  = 1 kilogram or 1000 grams and so on

See below presentation regarding the actual weight of water and bottle to determine their exact weight in Kilograms.

Weight of bottled water filled in full

If you put a 0.6 liter of bottled water filled in full on a weighing scale, expected reading should be 627 grams or 0.627 Kg.
Weight of an empty bottle
Weight of an empty bottle only which is equal to 20 grams or 0.020 Kg

0.6Liters =  600 ml or 600 grams

Gross Weight  = 627 grams >> weight of bottle and water

Approximate weight of the bottle only  = 20 grams

Tare weight = (627 – 600) =607 grams >> expected weight of the water only

That is how simple it is. But considering also the weight of the bottle which is approximately 20  grams on a 500 to 600 ml bottle. So we expect if we weigh a full 600 ml bottle, it should be within 620 to 630 grams (bottling company has also an inaccuracy in their refilling process).

If it happens that the bottled water is not newly purchased and unopened, just a refill until the very top,  we will expect an error of 30 grams so it reads at least 630 grams (this is what we call gross weight). Since we know the error, just subtract this to the total weight then you have your expected weight.

Since we know this already, every time we go to the market and not sure about a certain weighing scale, “just put your bottled water first before they put the meat or what is needed to be weighed.”  This way, you are making a verification to make sure that the reading is accurate as expected, in this way, you get what you have paid for and create a win-win situation.

ok-sign

By the way, in order for us consumers to be protected from this kind of problems, the government has a body or organization monitoring all measuring instruments or devices that are used for the public which includes gasoline and water meters.

These are under what we call Legal Metrology. In the Philippines, legal metrology is under a national laboratory called Industrial Technology Development Institute (ITDI) which are then connected to Department of Trade and Industry ( DTI). If a weighing scale that is not calibrated and it is being used in public, you can file a complaint to them.

To learn more about what accuracy and precision with regards to calibration, please visit this page https://calibrationawareness.com/

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Are there any other things that are practical to use? Leave a comment and subscribe.

Best Regards,

Edwin

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