The settings available from the Dash Scale pane control the scale applied to the dash pattern for dashed entities.

Dialog Options:

Not Scaled

No scale factor is applied to the dash sizes.

Mapped by Flag/Pen Number

The values of the dash sizes (as specified on the general page) are multiplied by the scale factor for the entity's flag/pen number.  A value of 0 means no scale factor in a possible range of 0 to 2.0. 

Mapped by Color Number:

The values of the dash sizes (as specified on the general page) are multiplied by the scale factor for the entity's color number.  A value of 0 means no scale factor in a possible range of 0 to 2.0.  To set the scale factor for a color number, select the color number in the grid, and enter the value in the edit field.  The colors in the palette are for reference only, and will display the colors specified in the palette on the Color page.