Weight Variation by Latitude

Weight Variation by Latitude refers to the claims that scales have measured masses to weigh up to 0.5% less near the equator compared to the polar areas. It is asserted that this is due to a combination of the centrifugal effect from the rotation of the earth and the increased mass at the equator.

Upon assessment of the experiments supporting this, it is found that these experiments are conducted with the scale and test body exposed to the surrounding atmosphere. A scale is calibrated for one area and then taken to another area, uncalibrated. Measures are not taken to isolate the test body and the measuring device from the influences of the environmental atmosphere. It is known that pressure and humidity affects scales. It is also known that that pressure is greater at the poles and lesser at the equator. It is further known that pressure is greater at lower altitudes near sea level and lesser at higher altitudes. Humidity likewise has a relationship with the latitudes and altitudes.

Andrew Huszczuk, Ph.D., writes (Archive):

Precision Scales
From Drift in Measurements with Analytical Balances (Archive) we read:

One precision scale manufacture lists many factors (Archive) which can affect a scale:

Factors That Can Affect Your Scale’s Accuracy

If the air pressure from the calibration environment is different than the operating environment, it will affect the scale. Also listed on the page are temperature and humidity which can affect the operation of a precision scale.

Standardscale
Standardscale.com says (Archive):

How does the environment affect weighing on a lab balance?

Industrial Scale Comany
The Industrial Scale Company tells us (Archive):

Sources of Error in Weighing Instruments

Bathroom Scales
Inconsistent scale readings are also readily seen at home in bathroom scales. If left uncalibrated, the reading can vary.

Can I Trust My Bathroom Scale? (Archive)

Uncalibrated Scale Drift
On the topic of uncalibrated scale drift precisionscale.com portrays a 0.5% variance as small, and gives it as an example of why calibration is necessary.

https://precisionscale.com/scale-calibration/ (Archive)

Understanding the Importance of Scale Calibration

Legitimate Measuring Device
In fact, in the EU if a scale is not calibrated before use after repositioning then it is not considered to be a legitimate measurement device. From a precision scale manual we see:

https://www.soehnle-professional.com/documents/all/406/Manual_9437_EN.pdf (Archive)



Kern Gnome Experiment
The precision scale manufacturer Kern conducted a public test of the variation of weight by latitude, showing that weight changed when a resin composite gnome and one of its precision scales were sent to members of the public at different latitudes:

Website: http://gnome-experiment.com/ (Archive)



Scale Not Calibrated
The scale was calibrated in Germany and then sent to different areas:

https://www.chemistryworld.com/news/gnomadic-experiment/4924.article (Archive)

Long weigh from gnome: The bizarre experiment where a garden ornament travels the world to measure gravity (Archive)

Procedure
Members of the public were instructed to place the gnome onto the scale and to record their results:



Spring Scale Experiment
The Spring Scale Experiment shows a similar methodology of calibrating in one area and taking to another:

http://physicstasks.eu/930/spring-scale-on-the-pole-and-on-the-equator (Archive)



The book Practical calculations for engineers (Archive) describes the same method:

Worldwide Air Pressure Gradient
The following sources explain that air pressure has a relationship with latitude, being lower near the equator and greater near the poles:

https://www.pmfias.com/pressure-belts-pressure-systems-equatorial-low-sub-tropical-high-sub-polar-low-polar-high/ (Archive)

World Distribution of Sea Level Pressure

and further down:

https://en.wikipedia.org/wiki/Polar_High

Worldwide Humidity Gradient
Humidity, like temperature and pressure, has a relationship with the equator as well:

https://en.wikipedia.org/wiki/Humidity#Climate

Addendum
When one examines the properties of the air they will find that other elements too are related to pressure, temperature, and humidity; such as air viscosity and thermal diffusivity -- all of which may affect the operation of scales complex ways. If a scale is affected by any of that then those factors should be excluded, ideally in a vacuum chamber experiment which demonstrate the matter emperically. Merely claiming or asserting that there are no factors that affect the device is insufficient. Yet, a search for examples of this experiment conducted in a vaccum chamber finds none.

Any singular assessment appears insufficient. It is due to the complex nature of the air that scale manufacturers and metrologists recommend calibrating often, whether a scale is indoors or outdoors. Indeed, a company's failure to calibrate its scales in certain fields can result in fines and even legal action.

Adopting this basic and reasonable level of scrutiny, an experiment which is based on bringing uncalibrated scales to different environments and then looking for differences of a fraction of one percent of a body's weight must only be questioned for validity. The European Union has mandated that any scale that is not calibrated after being relocated is not a legitimate measurement device. Insisting that one can move such a device without control of the environment is an offence against both reason and regulation.

Historical Fudging
Of interest, upon reviewing the history of weight changes by latitude we find that the nature of the Earth was modified because the theory did not meet the data. This is the origin of the flattening of the poles.

From Voltaire we see (Archive):

Hence, the theory was changed to fit the result, giving us a round world with flattened poles. However logical a bulging equator is in concept, the ability to change a theory to meet a desired result exists as a fudge factor. Had the results been any more or less different, the theory or associated theories would have been changed to fit those results, either by bulging out the equator more or less to fit the data or by looking for other elements to modify.

Time Dilation by Latitude
In contradiction to an uncontrolled three hundred year old practice of bringing weighing devices to different environments and adapting the theory to fit the results, other situations involving devices which are not affected by atmosphere do not show changes by latitude. See: Time Dilation by Latitude