![A fence made out of giant pencils](https://wild.maths.org/sites/wild.maths.org/files/media/photos/section_photos/Freedom_constraints/wide_Fencils16by9.jpg)
You can use rods of lengths 3, 4 and 6 units to measure different lengths.
The diagrams shows how to measure lengths of 1, 3, 5 and 7.
Can you see how to measure a length of 2?
There are rods for 4 and 6, so it's possible to measure all the lengths from 1 to 7.
Can you convince yourself you cannot measure a length of 8?
![alternate](/sites/wild.maths.org/files/combining_rods_2.png)
Can you find another set of three rods that can be used to measure all the lengths from 1 to 7?
What about 1 to 8?
1 to 9?
1 to ...?
How far can you go? Take a look at Longer and Longer to explore further.