Change dip amount                              Change strike direction 

Strike and dip symbols are used on geologic maps to show the orientation of a rock layer.  In this movie, a rock layer is represented by the tilted plank of wood with a strike and dip symbol on top.  The longer line represents the direction of strike and is always parallel to the water line, because the strike represents a horizontal line.  The smaller line indicates the direction of dip and is perpendicular to the strike line; it shows the direction in which the layer is inclined.

As you spin the plank, the strike and dip symbol tells you the orientation of the plank. The plank can be spun in 30° increments, and tilted in 15° increments of dip, from 15° to 90° (vertical).