Something weird I have observed over the last few years. When I weigh myself in Japan (where I live) I get Xkg weight. When I weigh myself in Australia (where I am from) I get X-2kg weight. At first I just thought my home scales in Japan were wrong as all the scales in Australia, including a medical scale, gave the same reading (x-2kg). But then my wife who get weighed at the hospital every month due to her pregnancy found that the hospital scale and the Japanese scale we have at home were almost identical.
So what’s going on?
Just to be clear I’ll use real weights. In Australia when I weigh myself it says I weigh 90.5kg. In Japan I get 92.5kg. Its always exactly a 2kg difference.
Assuming QED ain’t whooshin’, I doubt that it’s caused by the variation in the Earth’s size (using the numbers in QED’s cite that would make for about a 0.7% difference). And it wouldn’t make it exactly 2kg each time.
So try a test - find something with a known weight (a lab weight would be nice but 1L of water should do it) and stick that on your scale. What does it say? To be thorough, repeat with increasing masses and see how the error varies.
I’m guessing that one of your scales is just off by 2kg.
Balances measure mass, which isn’t affected by gravitational forces like measurements of weight are, so if your home-based scale’s weight (most home spring-based balances measure force) agreed with the balance at your doctor’s office, then it is properly calibrated to estimate your mass. Differences in altitude cannot account for a 2 kg difference in weight.
A good way to test if the scales are really different, or you are just measuring fluctuations in weight (time of day, water consumption?), would be to weigh your suitcase just before leaving your home, and upon arriving at the new location (assuming the contents haven’t changed).
There are other things that can cause a 2 kilogram difference in weight. Especially in pregnant women. It could be something as simple a weighing ones-self before or after a meal, before or after going to the bathroom, even stress can cause people to weigh more than relaxed individuals.
It would be very difficult to move a person between Australia and Japan without letting a couple percent chang creep into their weight. Even if you are very regular in your habits and let temporary effects settle out, what if the water salinity is different in your two habitats, and there’s a minor change in your level of hydration, for example?
Transporting a scale in a vibrating airplane could easily mess with its calibration, too.
Now, if you could weigh an accurate standard in each place, or maybe even the same standard, then we’d have more convincing evidence.