Science moves on. Time is now defined by readily available clocks
that use caesium atoms as their pendulums, while distance is
specified in terms of the speed of light in metres per second (the
caesium atoms having already provided the value of a second), and
these days that speed can be measured with great accuracy using
easily purchased equipment. Mass, however, remains stubbornly
stuck in Paris, under three concentric glass lids (pictured)
strangely reminiscent of cheese covers, which are intended to stop
it either absorbing or shedding matter and thus changing in value.
Unfortunately, the cheese covers have not worked.