What is the difference between 00.0 and OFF next to the blade icon on the LCD screen?

The blade icon indicates the compensation for the blade width in measurements.  Both can be accessed from the angle selection menu (00.0 is the default and OFF is at the end after 60.0).

When the 00.0 is displayed, the blade offset is active (at whatever the saved value is) and will be applied every-time the zero button is pressed.

When the OFF is displayed, the blade offset is still saved to the tool, but not active for the current measurement.  This is useful when making slots or when you want to make a cut and have the scrap on the right side of the saw blade.