Maths/ Apparatus to scale an image - London Science Museum

I visited the Maths section of the Science Museum in London recently. I've always found the interplay of engineering and maths interesting. Here is a Flash recreation of one exhibit - a simple but clever apparatus which uses the idea of similar triangles to accurately scale an image.

Use the right-hand pen to trace around the green image. Use 'pen up' and 'pen down' to lift the pen from the paper and put it down again.

The second pen traces out a scaled version of whatever you draw. The percentage scale factor can be changed by adjusting the position of the second pen along its rod. The code automatically adjusts the left-hand pivot in order to create a pair of similar triangles.

Click here to see photos of the Science Museum exhibits