The Screwdriver/Ruler tool is only found on some larger 58mm Victorinox models.
It has a flat screwdriver tip on the end of a plain blade that is marked in inches and metric on one side and is blank on the other side.
Some screwdrivers, on an early version, or by mistake, did not have the ruler markings!
Note: On most 58mm models the screwdriver tip is found on the end of the nail-file tool - for instance the Classic SD.