Hi Peter. 48 it the lowest speed the real Hornet HUD can show. You can see this in this video for example:
http://www.youtube.com/watch?v=Mkx4C5SEej0Even if it did show a lower reading, that would be your air speed, which when on the carrier deck, will be the speed of the carrier +/- the wind speed, and it will still not be a good indication of your taxiing speed. However, there is a Nose Wheel Steering cue displayed in the lower right corner of the HUD. If it shows 'NWS HI' - this means that your taxiing speed is low enough so that you can apply full deflection of the nose wheel. If it shows only 'NWS', this means your taxiing speed is too high and you should use a much smaller deflection. So to avoid flipping during taxiing, make sure you see the 'NWS HI' cue.
The NWS cues in the real Hornet indicate in which of the two modes the Nose Wheel Steering system is - low gain ('NWS' cue) or high gain ('NWS HI'). In the low mode ('NWS'), full rudder pedal deflection commands approx 16