Under weight packaging

HillStreetBlues

molerat said:

HillStreetBlues said:

QrizB said:

HillStreetBlues said:

Ergates said:

The other thing to do before raising this anywhere is to calibrate your scales (kitchen scales aren't always very accurate).  Easiest way to do this is with a known volume of water.

You can't calibrate scales that way, the volume of water will change with the temperature.

It changes by less than 1% between 0C and 40C. It's likely to be good enough for kitchen scales.

https://www.internetchemistry.com/chemical-data/water-density-table.php

It still doesn't make it a good way to calibrate something, why use something can vary, never mind the fact you have to accurately measure the water in the first place.

Where are you going to get a known volume of water - a bottle of water is going to be measured to the same tolerances as anything else -  or where are you going to get your jug calibrated ?

All I know is my kitchen scale give the same to the gramme as my local PO

Don't know why you're asking me? I'm the one stating it's a bad idea

Okell

molerat said:

HillStreetBlues said:

QrizB said:

HillStreetBlues said:

Ergates said:

The other thing to do before raising this anywhere is to calibrate your scales (kitchen scales aren't always very accurate).  Easiest way to do this is with a known volume of water.

You can't calibrate scales that way, the volume of water will change with the temperature.

It changes by less than 1% between 0C and 40C. It's likely to be good enough for kitchen scales.

https://www.internetchemistry.com/chemical-data/water-density-table.php

It still doesn't make it a good way to calibrate something, why use something can vary, never mind the fact you have to accurately measure the water in the first place.

Where are you going to get a known volume of water - a bottle of water is going to be measured to the same tolerances as anything else -  or where are you going to get your jug calibrated ?...

This ^

I worked as a trainee trading standards inspector for a couple of years in the 1980s.  The only things I learned of any value were (1) I didn't want to be a TS inspector, (2) the theory of measuremant error, and (3) the importance of reliable reference measures.

As I don't carry reliable reference weights around with me, the only real precaution I take when using supermarket scales is to check they are zeroed properly before using them.

I also regularly check the weights of prepacked produce at home and I don't think I've ever come across a case where the item weighed less than it was meant to.  They are almost always overweight or spot on - to within a reasonable margin of error.

(Before I quit smoking I also regularly used to count the number of matches in a box.  Just to be sure... )

Okell

HillStreetBlues said:

molerat said:

HillStreetBlues said:

QrizB said:

HillStreetBlues said:

Ergates said:

The other thing to do before raising this anywhere is to calibrate your scales (kitchen scales aren't always very accurate).  Easiest way to do this is with a known volume of water.

You can't calibrate scales that way, the volume of water will change with the temperature.

It changes by less than 1% between 0C and 40C. It's likely to be good enough for kitchen scales.

https://www.internetchemistry.com/chemical-data/water-density-table.php

It still doesn't make it a good way to calibrate something, why use something can vary, never mind the fact you have to accurately measure the water in the first place.

Where are you going to get a known volume of water - a bottle of water is going to be measured to the same tolerances as anything else -  or where are you going to get your jug calibrated ?

All I know is my kitchen scale give the same to the gramme as my local PO

Don't know why you're asking me? I'm the one stating it's a bad idea

Yeah - I thought it was a bit harsh!   

HillStreetBlues

Okell said:

This ^

I worked as a trainee trading standards inspector for a couple of years in the 1980s.  The only things I learned of any value were (1) I didn't want to be a TS inspector, (2) the theory of measuremant error, and (3) the importance of reliable reference measures.

As I don't carry reliable reference weights around with me, the only real precaution I take when using supermarket scales is to check they are zeroed properly before using them.

I also regularly check the weights of prepacked produce at home and I don't think I've ever come across a case where the item weighed less than it was meant to.  They are almost always overweight or spot on - to within a reasonable margin of error.

(Before I quit smoking I also regularly used to count the number of matches in a box.  Just to be sure... )

I worked in a pharmaceutical company and one of my jobs at times were to test the calibration of the many scales with a set of weights. When it closed down I was going to liberate them, but someone beat be too it.

Ergates

HillStreetBlues said:

QrizB said:

HillStreetBlues said:

Ergates said:

The other thing to do before raising this anywhere is to calibrate your scales (kitchen scales aren't always very accurate).  Easiest way to do this is with a known volume of water.

You can't calibrate scales that way, the volume of water will change with the temperature.

It changes by less than 1% between 0C and 40C. It's likely to be good enough for kitchen scales.

https://www.internetchemistry.com/chemical-data/water-density-table.php

It still doesn't make it a good way to calibrate something, why use something can vary, never mind the fact you have to accurately measure the water in the first place.

Because it's cheap (practially free), easy, uses readily available materials and equipment that everyone will already have in their homes and the margins of error are small enough as to make absolutely no difference for the degree of accuracy both needed and achievable with home kitchen scales.

The density difference between water coming out of the tap and at room temperature is less than 1%. To suggest this would introduce an inaccuracy whilst calibrating kitchen scales is *utterly* absurd.

Put a measuring jug on the scales, zero it, fill it up to the 1000ml mark, put it back on the scales. 

If you scales say it weights around 1000g then they're good enough.

Okell

Ergates said:

HillStreetBlues said:

QrizB said:

HillStreetBlues said:

Ergates said:

The other thing to do before raising this anywhere is to calibrate your scales (kitchen scales aren't always very accurate).  Easiest way to do this is with a known volume of water.

You can't calibrate scales that way, the volume of water will change with the temperature.

It changes by less than 1% between 0C and 40C. It's likely to be good enough for kitchen scales.

https://www.internetchemistry.com/chemical-data/water-density-table.php

It still doesn't make it a good way to calibrate something, why use something can vary, never mind the fact you have to accurately measure the water in the first place.

... Put a measuring jug on the scales, zero it, fill it up to the 1000ml mark, put it back on the scales. 

If you scales say it weights around 1000g then they're good enough.

Assuming the 1000ml mark is in the right place...

user1977

Okell said:

Ergates said:

HillStreetBlues said:

QrizB said:

HillStreetBlues said:

Ergates said:

The other thing to do before raising this anywhere is to calibrate your scales (kitchen scales aren't always very accurate).  Easiest way to do this is with a known volume of water.

You can't calibrate scales that way, the volume of water will change with the temperature.

It changes by less than 1% between 0C and 40C. It's likely to be good enough for kitchen scales.

https://www.internetchemistry.com/chemical-data/water-density-table.php

It still doesn't make it a good way to calibrate something, why use something can vary, never mind the fact you have to accurately measure the water in the first place.

... Put a measuring jug on the scales, zero it, fill it up to the 1000ml mark, put it back on the scales. 

If you scales say it weights around 1000g then they're good enough.

Assuming the 1000ml mark is in the right place...

Obviously you've calibrated the jug by using the scales....

HillStreetBlues

user1977 said:

Okell said:

Ergates said:

HillStreetBlues said:

QrizB said:

HillStreetBlues said:

Ergates said:

The other thing to do before raising this anywhere is to calibrate your scales (kitchen scales aren't always very accurate).  Easiest way to do this is with a known volume of water.

You can't calibrate scales that way, the volume of water will change with the temperature.

It changes by less than 1% between 0C and 40C. It's likely to be good enough for kitchen scales.

https://www.internetchemistry.com/chemical-data/water-density-table.php

It still doesn't make it a good way to calibrate something, why use something can vary, never mind the fact you have to accurately measure the water in the first place.

... Put a measuring jug on the scales, zero it, fill it up to the 1000ml mark, put it back on the scales. 

If you scales say it weights around 1000g then they're good enough.

Assuming the 1000ml mark is in the right place...

Obviously you've calibrated the jug by using the scales....

Better to use a second pair of scales to calibrated the jug.

Ergates

Okell said:

Ergates said:

HillStreetBlues said:

QrizB said:

HillStreetBlues said:

Ergates said:

The other thing to do before raising this anywhere is to calibrate your scales (kitchen scales aren't always very accurate).  Easiest way to do this is with a known volume of water.

You can't calibrate scales that way, the volume of water will change with the temperature.

It changes by less than 1% between 0C and 40C. It's likely to be good enough for kitchen scales.

https://www.internetchemistry.com/chemical-data/water-density-table.php

It still doesn't make it a good way to calibrate something, why use something can vary, never mind the fact you have to accurately measure the water in the first place.

... Put a measuring jug on the scales, zero it, fill it up to the 1000ml mark, put it back on the scales. 

If you scales say it weights around 1000g then they're good enough.

Assuming the 1000ml mark is in the right place...

It's easier to produce an accurate jug (all molded plastic jugs created from the same press will be the same size) than it is to create and calibrate a set of electronic scales.

Moreover, short of visible physical damage, the accuracy of a jug will not change over time - unlike scales which drift  (hence the need to recalibrate them in a lab setting).

More moreover, the OP to this thread was complaining about chicken livers weighing 350g instead of 400g - more than 10% off.    A calibration using volume of water in the kitchen is more than accurate enough to determine if the scales are working correctly to that degree.

Murphybear

Heavens!  I’m sure I did things less complicated than some of this when doing my Physics degree 

Kitchen scales don’t really need to be that accurate.  I use my kitchen scales a lot and have no idea how accurate they are.  My cakes and other bakes never suffered.