Hold out both hands like a see-saw. If a bag of sugar sat in one hand and a pencil in the other, which hand would drop down? And here is the tricky one: is a bag of sugar more than one kilogram, less, or exactly one?

Four weights on the dial, from lightest to heaviest. Look at where the needle points each time, and notice how far round it has moved as the weight gets heavier. When the needle reaches the very top mark, that is one whole kilogram: 1 kg = 1000 g.

Today we weigh real things. Your group uses its own scales for this. We will feel each one in our hands first and guess, then set it on the scales to check: an apple, a copybook, a lunchbox, and a bottle of water. Feel before you read the dial each time.

Set out four station objects around the room, one for each group to start at: a rubber, a full pencil case, a library book, and a one-litre bottle of water. Feel your object, guess grams or kilograms, then weigh it at your group's scales and write the reading. When you hear the signal, every group moves on to the next station. As a stretch, put all four in order from lightest to heaviest by their weights.