Speed travelling at/Speed zone?

I have a TOMTOM ONE 3rd Edition - we find it to be a marvellous gadget. However, one very small problem:- When I have a destination entered and am driving there are lots of icons and numbers below the map. The one which shows my speed of travel/speed limit of area is showing 23/29; 23/39; 23/49. The speed limits of 60 and 70 show up correctly.

Any idea.

Many thanks
Barrie H Anderson