Your whole premise is flawed.
Show a real example of that, not one you made up.

We can immediately dismiss your first two prices, if you can't work out that £1 is 100p, you shouldn't be allowed in a shop by yourself anyway.

In the unlikely even something is expressed in pence/gram, it is certainly not going to be a tomato.

You have identified a simple fact, that we can all usually understand. Different items come in different measures.

Go to Sainsbury's, find us a comparable product that you can't compare (you won't find one). There's no need to compare a jar of freeze dried coffee with a box of washing powder - that's what you're trying to claim you should be able to do.
(username failed moderation, Fri 23 Sep 2011, 12:21, 1 reply)

(sigh)
Sainsbury's Borough High street.
Sep. 23 2011, 15:45ish

Helmans mayonnaise.
Jar £(price) for 400g
Squeezy bottle £(price) for 430ml.

I don't know the density of mayo...
( DukeEuphoria Comes highly reccomended, Fri 23 Sep 2011, 16:02, closed)

See, all you have to do
in your head, is to divide the first price by 400 and the second price by 430 to find the price per ml. I know it's only pennies, but...
(Che Grimsdale Best before:, Fri 23 Sep 2011, 16:35, closed)

So mayo has the exact same density as water now?
How useful, I'd always thought it would be different somehow, what with it not all being water.
(Me, I'm not... in any way intoxicated, Fri 23 Sep 2011, 17:39, closed)