This guide describes how to construct and use a simple device known as a 'bunjip'. The bunjip is used like a massive spirit level and enables you to accurately measure the differences in height between different points. This information could be used to calculate gradients or plot contours. It has a wide variety of applications - it could be used to measure the head on a hydro electric system; or when creating a base map of a permaculture garden; or to check that the tops of upright posts are level during construction.

You will need

1. A long piece of clear flexible plastic pipe, over 20ft long.
2. Two lengths of wood about 6ft long each.
3. Some string, cable ties or adhesive tape.
4. A permanent marker pen or paint.
5. A squeezy bottle - such as a used washing up liquid bottle.

What you do

1. Choose a unit of measurement - such as inches or centimetres - and mark the wooden lengths to create two giant rulers that measures from the ground (zero) to the top (72 inches / 200cm).

2. Attach the plastic tube to the wooden lengths so that the ends of the tube extend a short distance past the top of your rulers. The tubes should also be fixed along the length of your rulers but don't need to be fixed all the way to the ground.

3. Fill the tube with water using the squeezy bottle until the water can be seen at the level of the mid point of your rulers (eg. 36 inches / 100cm). You may have to pour some out to get this accurate.

Note: Obviously the longer the pipe you use, the greater the distances between the points that you can measure in one go. If you can't get a long length of clear pipe, you could use two 6 ft lengths joined by garden hose, since it only needs to be clear at either end. Food colouring may be used to make the level easier to see.

How you use it

You need at least two people to operate the bunjip. A third would be useful to write down the information or place stakes in the ground as contour markers etc.

Each ruler is held upright by one person with the base place on the ground. When both rulers are on the same level, the water in the tubes will be level with the same markings on each ruler.

When one of the rulers are at a different level, the water will be seen to be at different levels on the rulers. The difference between the readings on the rulers provides you with the difference in level at which the rulers are placed.

You can find contour lines by walking and marking the points at which there is no difference between the levels of the rulers.

You can measure the difference in height between two points or objects by having the rulers placed on each point and noting the difference. When the points/objects you wish to measure are further apart than your tube will allow you to cover, you will need to cover the distance in stages.

Important: Don't let the difference in height become greater than the length of your rulers or you will spill the water. Don't lay the rulers down, lean them against something when you are not using them.