I am holding a bag of sugar in one hand and an apple in the other. One of them is a kilogram and one is only a couple of hundred grams. Just by lifting them, hands up: which one do you think is the kilogram, and how did your hand help you decide?

Reading a weighing scale

Watch the scale at the front as I weigh four things. First an apple: the needle settles near 200 g. A gram is our small unit, so light things are counted in grams. Predict before the next one: is a bag of pasta heavier or lighter than the apple?

Now the bag of pasta reads 500 g. Notice the needle points exactly at a marked line, so we read it straight off. Now the bag of sugar tips right over to 1 kg, our big unit, and it is the same as 1,000 grams.

Last of all the loaf. The needle does not sit on a big mark. It lands between two of them, so we count the small divisions to read it.

1. Name the two big marks the needle sits between: 700 g and 800 g.
2. Check how the gap is split. On this scale there are two equal small steps between those marks, so each small step is worth 50 g (half of 100 g).
3. Count how many small steps the needle has moved past the lower mark. It has moved one step past 700 g.
4. Add that on: 700 g + 50 g = 750 g.

So the loaf weighs 750 g. Whenever the needle lands between marks, use this same four-step count.

Now we weigh together at your tables. We weigh these four items in this order: a rubber first, then a full pencil case, then a hardback book, then a schoolbag. Before each one goes on the scale, we say our estimate out loud, choosing grams or kilograms, and then we read the scale and see how close we were. Write each estimate and reading on your Weighing Record Sheet as you go.

Now it's time to compare and put weights in order. A fresh set of objects will come round the room: a small water bottle, a tin of beans, a bag of oranges and a big dictionary.