This property should be set to values between 0 and 180, or 255, as explained below:
Zero means no rotation.
1-90 means 1 to 90 degrees counter-clockwise (90 causes text to be displayed in the vertical direction going up the cell).
91-180 means 1 to 90 degrees clockwise (180 causes text to be displayed in the vertical direction going down the cell).
255 causes letters to be stacked top to bottom and not rotated.
The rotation always zero if the horizontal alignment is set to Fill or Selection.