Road speed warning on dashboard

[Crossland bassboy]

Hi. Could someone please reply to this question. When I pass a speed sign eg, 30 or 40, it displays on the dashboard but only for around 100 yards or so then reverts back to a red circle with 2 dashed lines. Unless the car sees another speed sign soon after then displays that speed. Does this normally happen that the speed sign only on for a few yards,   can the dashboard be set up so it displays all the time only change when the road speed sign changes.  I'm getting old and i need to be reminded. 

Many thanks