Tutor’s Toolkit: Application of Number

Interpreting Information

I5	Read scales on a range of equipment to given levels of accuracy

I5.1	Reading from scales

Scope: 

Students need to be able to:
•	read quantities from a variety of scales,
•	read correctly chosen quantities from twin scales,
•	convert between different units using a twin scale.

What students need to know:

When you look at a dial or a scale, the important thing to look for is how many ‘intervals’ there are between two numbered markers. An ‘interval’ is the gap between two adjacent markers. You can then work out how much each un-numbered mark is worth. To make things harder, sometimes the arrow points to a place between the marks!

For example:

This scale has ten intervals between 38 and 40.
That’s 2 units divided into ten parts.
So, each interval must be worth 0.2.

Scale reading 1

On this scale, the arrow is pointing to 38.4

Scale reading 2

This arrow is between two marks.
The slightly longer middle mark is at 39.
The arrow is pointing to 39.1

Scale reading 3

Between these two arrows there are 3 intervals.
That’s 0.6.

Scale reading 4

This tank holds 64 litres.
There are 4 intervals between 0 (empty) and 64 (full).
Each interval is 64  4 = 16 litres.
So, the arrow is showing 16 x 3 = 48 litres.

Scale reading 5

This is a car speedometer. 
It shows mph (miles per hour) and km/h (kilometres per hour).
On the mph scale there are two intervals between 0 and 20. 
Therefore, each mark must be 10 mph. 

The indicator (the dotted line) is showing 55mph on the mph scale.
It is showing slightly less than half way between 80 and 100, so slightly less than 90. 
Let’s say 88km/h on the km/h scale.

You can use the speedometer to convert between mph and km/h.
Look on the km/h scale at 60km/h.
Below this is a little less than 40, let’s say 37 on the mph scale.
So, 60km/h = 37mph.