When we measure something we're finding a number that represents the distance of an object. When we measure a length we have to make sure we're going from one end of an object to the other end, it doesn't matter if it's sideways (horizontal) or up and down (vertical).
When we measure we need to think about the units. Are we measuring in millimetres, centimetres, metres, kilometres, inches, feet or maybe yards?
It's really important to know the unit, $1$1 metre is much shorter than $1$1 kilometre!
We need to make sure that we measure the full length of an object. If you measure your height, you make sure you're standing up straight. If you were sitting or hunched over would the height measurement be accurate?
If we're using a ruler to measure, we need to make sure we're starting from zero. Some rulers have some space before "0." If we're using a ruler we also need to think about which end of the ruler we're using.
This kangaroo picture is next to a centimetre ruler.
How tall is the kangaroo in centimetres from its ears to its toes?
What is the length of the shaded bar in the image shown?
Write down the measurement marked with an X.