After MC Newberry's excursion into the niceties of English grammar ( Knowing the Difference), I couldn't resist:-

The grocer's apostrophe,

Once the domain

Of dry academics

Who'd quietly complain,

Is nothing compared

To the pain we endure

Now that we can't weigh

In pounds anymore.

The little, old lady,

In metric unsound,

Asked for her carrots

In old fashioned pounds.

"Oh Ma'am," said the grocer

"That really won't do!

We only have kilos

Now everything's new."

"Oh dear," sighed the lady,

And trying to please:-

"I'll just have a pound

of your kilos then, please."