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.