Don't make the mistake of guessing a gradient

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You may think you can judge the gradient of a paths slope by sight alone, but your guess will be inaccurate. Even the most experienced path surveyors will get it wrong.

Always use a clinometer to measure the gradient of a paths slope. A clinometer is a hand held instrument used for measuring a gradient in degrees or percentage.

clinometer

To measure the gradient of a paths slope requires both the observer (the person holding the clinometer) and target to be a constant height above the ground, so generally a height of measurement stick (a range pole) is used to measure gradients. But if you do not have a range pole, you can use a person instead, preferably of the same height, to be the height of the measurement stick.

How to measure a gradient

To meaure a gradient, you will need to complete the next three steps:

Step 1 Familiarise yourself with the clinometer

Hold the clinometer to your dominant eye (see 'Which eye is dominant?' below). With the dominant eye open and the other eye closed, look into the clinometers' viewfinder. The first thing you will notice is a rotating scale. There are numbers printed on both sides of the scale. The left side is in degrees and the right side is in percentages. By rotating the clinometer all the way towards the sky, you will see labels identifying the degree and percentage scales. Take a minute to get familiar with the clinometer. You will notice the horizontal line in the centre of the viewfinder. This is the line you will use to measure gradient. As you move the clinometer up and down, the scale will move while the horizontal line stays put.

Which eye is dominant?

Try using the thumb test. Stick your thumb up at arm's length in front of your face. With eyes open, line up your thumb with any target in the background (for example, a tree or post). Close one eye, then open it and close the other eye. Your thumb will appear to move. Determine which eye does not move your thumb. That is your dominant eye.

Step 2 Locate the target ('zero point')

Once familiar with the clinometer, it is time to locate the target ('zero point') on a person or a height of measurement stick (a range pole).

With a range pole:

Place range pole upright in the ground. Stand tall, facing the range pole with the pole up against your face. With your hand, locate your eye height on the pole, and then, with coloured tape mark your eye height onto the pole to make it easily visible from a distance. The coloured tape mark is the target ('zero point'), that you will line the clinometer with, to measure the gradient.

With a person:

Using another person, preferably of the same height, stand 10 to 20 metres apart on level ground. Face the person and hold the clinometer to your dominant eye with your opposite eye closed. Find the 0s, line them up with the horizontal line, and open your other eye. Binocular vision will superimpose the line across the persons face. The point where the horizontal line intersects the persons face is your target ('zero point'). This is the spot you will be focusing on to measure a gradient.

If you are the same height as the person, the target ('zero point') will fall across their eyes. If you are taller, the line will be above their eyes. Don't forget where the target ('zero point') is, and remember to always stand tall when reading gradients. If you start to slouch throughout the day, the gradients that you read will be inaccurate.

Step 3 Measure the gradient with the clinometer

Ask the person to stand on the paths slope above you, or place the range pole in to the slopes surface. Stand on the path below facing the person or pole. Hold the clinometer to your dominant eye, and with both eyes open, put the horizontal line on the target ('zero point') mark on the person or pole. Now read the degree or percentage number on the scale. You have just measured the gradient of the paths slope between two points over a given distance. If you move closer to the person or pole, the gradient will be greater, and if you move further away, the gradient will be less. This is because the rise is constant, but the distance is changing.

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