It seems that Le Grand is Le Wrong!
The cylinder of platinum and iridium used as the standard definition of the weight is known as Le Grand K and kept under lock and key in a vault near Paris.
It was the object that scientists regarded as having a defined mass of exactly 1kg.
But it is drifting out of alignment with the copycat cylinders with which it was forged in London in the 1880s.
The drift of 50 parts in a billion, less than the mass of a grain of sugar, was first noted three decades ago and has continued.
But the difference can cause havoc for scientists who require precise definitions.
Yet another reason to not use the metric system!