Satnav speed limit

I have set my max speed to 54mph on my tomtom pro, even though my vehicle does 56mph, gives a bit of leeway with arrival time for the inevitable phone call from the office when asked “when you gonna get there”

Regarding actual road speed limits, the tomtom does tell me what the speed limit is on any particular road and consequently adjusts the arrival time due to the varying speed limits.
(Not sure about Scotlands 40mph on single carriageways)