Look at this jug. The water has stopped somewhere between the 200 ml mark and the 400 ml mark. It is past 200, but it has not reached 400.

Hands up: how could we work out exactly how much water is in there, when the line sits in between two numbers?

Four jugs on the board, one at a time. For each one, work out what each little step is worth by counting the marks between two numbers. Then read where the water stops and say it out loud. The reading stays hidden until we have all said it.

Watch the last one especially: the water lands exactly halfway between two marks, so its value sits halfway between them too.

Now we'll fill four jugs together, one at a time. Each one asks for an amount, like Fill the jug to 400 ml. Work out what one step is worth first, then drag the water up to that mark and press Check. The reading stays hidden until you check, so read the marks, not a number.

Today we read the jug at group stations. Each group has its own jug and water tray. After each careful pour, work out one step and read the level. First fill to 200 ml. Then top up to 500 ml. Then pour some back to 300 ml. Last, fill right up to 1 litre.