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How tall is Severndroog?
Information for teachers
Severndroog Castle is very tall, but can your class find out exactly how tall?
Before visiting, ask students to brainstorm as many different ways as possible of estimating
the height of Severndroog. These might include
 just guessing
 measuring the height of one brick, and trying to count how many bricks to the top of
the castle, then multiplying the brick’s height and number
 measuring the height of the tallest student, then trying to work out how many times
that person would fit into the height of the castle, and multiplying the student’s
height and the number
 taking a ball of string to the top of the castle, tying a weight to it and lowering it to
the ground, then measuring the string used.
Students may come up with other ideas. Ask them to list all the suggestions.
When you visit ask your class, working in small groups, to test out each of the class
suggestions. How many are practical? Each group should record the results of each test,
and compare results. How similar are they? Does one method stand out as more reliable
than all the rest?
(Before using the ball of string approach, check with the staff on site to ensure the safety of
your class and other visitors.)
More accurate measuring using a clinometer
Extend this activity by using a clinometer to measure the height of the castle more
accurately. You may want to use a ready-made clinometer, or to borrow one from the
learning resource box at the castle. Making a clinometer in class, though, will reinforce the
principle of how this measuring device works.
Before you visit make sure your students know how to use the clinometer with confidence.
They should also understand scale, and be able to make a simple scaled diagram using
squared paper. Experiment with measuring the height of various structures such as tall
trees, your school building, tall lamp-posts. Get groups to compare their results and to try
to identify why there are differences, if any.
Severndroog Castle Building Preservation Trust
2014
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At the castle, divide your class again into smaller groups (four to five students). Each group
should have a clinometer, and a recording sheet. Disperse the groups around the castle’s
exterior, and ask them to measure 10 metres away from its base, marking the place
carefully. It is important that the spot is on the same level as the base of the castle.
Each member of the group will have a specific role
 looking through the clinometer to the top of the building
 reading the angle shown
 making sure the 10 metre distance from the tower is maintained
 measuring the height of the student using the clinometer (for complete accuracy this
should be the height of the student’s eyes above the ground.
 recording results.
It may be best to make several attempts at measuring the angle, for reliability.
Back at school, students should draw a right angled triangle to scale using centimetre
squared paper, deciding on the best scale to use.
 First draw the base of the triangle, which will represent the 10 metre distance, with
point A the place where the clinometer user stood and point B the base of the tower.
 Using a protractor draw in the angle at point A. Extend the second line/side of the
triangle from point A, and then draw in the third side using the squared paper to
ensure the angle at point B is a right angle.
 The height of the line BC now represents the height of the castle, which can be
calculated using the chosen scale.
 For accuracy, the height of the student who took the clinometer reading should be
added to the height of the castle.
 This process of measurement is called triangulation. This method is also used to
survey areas and calculate distance accurately. Severndroog Castle played an
important part in the surveying of south-east England and France.
 The castle was used in the 1790s as part of the survey linking London and France by
triangulation, with a 36-inch Ramsden theodolite, now in the Science Museum,
installed on its roof.
 Severndroog Castle is 19 metres, or 63 feet high.
 It is the highest point between South London and mainland Europe.
 In World War 2 it was used at a lookout point to warn of air raids.
Severndroog Castle Building Preservation Trust
2014