Here is a 250 ml glass next to a 2 l carton of milk. Capacity means how much a container can hold.

Roughly how many of those glasses do you think we could fill from one full carton? Have a guess before we work it out.

Look at the jugs in the picture. Read the level on each and notice how the marks are spaced — some count in 50 ml, some in 100 ml. Look closely at the top of the water: it curves up at the sides. That curve is the meniscus, and we read the flat dip in the middle, with our eye level with the mark.

One of you drives the jug on the board while the rest of the class calls out where the level should stop. You will set four amounts in turn, and each time the level has to climb further up the scale, so predict how far before it moves.

Keep the fractions of a litre in your head as you go: a quarter, a half and three quarters all have a mark of their own.

Today we set the level to match each target in turn: 100 ml, then 250 ml, then 450 ml, then 750 ml, and finally 1.25 l on the bigger jug. The 450 ml one lands exactly on a minor mark between the 400 and 500 marks.

The last target is on the bigger jug: its scale goes up to 2 l and its small marks jump by 100 ml, so read it more carefully. The level climbs a quarter past the litre line to 1.25 l.