They DID foresee that weight can vary. That's why they aren't measuring the weight of the masses. They are measuring the difference in their masses. They are using a highly accurate device equivalent to a double pan balance. If you place equal masses on each pan of a double pan balance, the needle points straight up. If one is more massive, the needle tilts to that side.
If you took equal masses to the moon and checked them on a double pan balance, they would be shown to be equal, even thought the gravitational field strength is different.
As several people on this thread have mentioned, the varying gravitational field is irrelevant in this comparison.
I'm suspicious of wording in the LA Times article versus your reply; you said what I wanted to hear.
From first paragraph of LA Times article :
In the more than a century since 'perfect' platinum-iridium cylinders were first used as the world's kilogram standards, their weights (emphasized by Amendment 10) have mysteriously fluctuated.From your reply:
That's why they aren't measuring the weight (emphasized by Amendment10) of the masses.Are physics flunkys at the LA Times screwing up the report?
Also, were the original masses calibrated in the same laboratory and then sent to remote locations? And were today's test masses also calibrated in the original laboratory, or were they calibrated at the locations where the original mass references wound up? Other possibilities?