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# Long description

Figure 12 A key identifies a small red ball as meaning 'O' and a slightly larger orange ball as meaning 'P'.

At the top of the diagram in part (a) there is an orange ball. Three lines radiate out and down from the orange ball, each ending at a red ball. Next to one of these lines it says 165.6 pm. From each red ball a line goes roughly vertically down. The angle between the lines above and below the red balls is shown as 127.0 degrees. Each vertical line ends with an orange ball. Between each of these three orange balls there is a red ball, a little lower down and a little further out. Each orange ball has two lines which go down and out to the red ball on either side of it, and the angle between these lines is shown as 99.5 degrees.

At the top of the diagram in part (b) there is a red ball. A line of length 143 pm goes vertically down to an orange ball. Three lines radiate out and down from the orange ball, each ending at a red ball. The angle between two of these lines is shown as 102 degrees. From each red ball a line of length 160 pm goes roughly vertically down. The angle between the lines above and below the red balls is shown as 123.0 degrees. Each vertical line ends with an orange ball. Three lines radiate out and down from each of these orange balls, each ending at a red ball. The three red balls which are in between two orange balls, have lines to the orange balls on both sides of them, while the remaining three red balls are connected to just the nearest orange ball.