[John Jorsett]

More likely that the magnetic/gravitational field of the earth has been changing over time. Also, the earth is viewed as a “geoid” as opposed to a constant sphere. a Geoid is somewhat “lumpy”. Also note that different locations over the globe have dfferent gavitic constants - theu, if we have a “known” mass and the gravitic constant for that particular region of the globe changes, that sample no longer “weighs” 1 KG.

Does that make sense?

The problem with that theory is that they collect the samples together in one place to compare them, and that's how they know they've changed. My guess is that some of the caretakers have been using them as paperweights.

[Nathan Zachary]

"The problem with that theory is that they collect the samples together in one place to compare them, and that's how they know they've changed. My guess is that some of the caretakers have been using them as paperweights."

well that settles it then, it's definitely a yet to be studied and explained sub-atomic decay. The reason each sample is slightly different is because they were never atomically identical as they thought.

Problem solved. /s

[PugetSoundSoldier]

My guess is that some of the caretakers have been using them as paperweights.

No, it's probably more along the lines of:

Why yes, that IS a kilogram in my pocket, but I'm still happy to see you!