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The normal tool displays a movable normal probability curve on
the graph view. (See below:) It displays the mean, standard deviation and area
under the curve.
Cursor
for normal tool:
Select the normal tool by clicking the
 button on the graph tools
tool bar, or by selecting the 'Normal' command from the 'Tools' menu.
When selected, the normal tool dialog box
is displayed (See below:).
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Drag on the title bar at
the top of the normal tool dialog box to move it.
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Check the 'Area = 1' check
box to set the total area under the normal tool curve to 1 unit.
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Check the 'Markers'
check box to display vertical lines under the normal tool cursor at
1, 2 and 3 standard deviations from the mean. (As in screen shot
above.).
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Check the 'Snap to grid' option to
locate the centre of the normal tool cursor (the mean) at the corner of grid
snap rectangles.
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Click the 'Cancel' button to stop
using the normal tool.
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Press the space bar on
the keyboard to plot a normal curve on
the graph view.
As the normal tool is moved on the graph view, the following information is
displayed in the normal tool dialog box:
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The mean of the distribution. This corresponds to the exact centre of the
normal tool cursor.
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The standard deviation (s.d.) of the distribution.
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The total area under the normal curve. (This will be 1 if the 'Area = 1'
check box is checked. (See above).
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Changing the shape of the normal curve:
With the normal tool displaying the normal curve on the graph view, click and
hold the left mouse button while moving the mouse.
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Drag the mouse horizontally to
change the standard deviation of the distribution.
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Drag the mouse vertically to
change the area under the normal curve. (Unless the 'Area = 1' check box is
checked, in which case the area is always 1).
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For fine
adjustment, hold down a Shift
key as well.
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