I have an in-built Nav unit in an almost new Citroen running latest mapping update . Unusually I have been visiting a number of unfamiliar local addresses in the following postcode areas: HP17, HP18, HP19, HP22, HP27, OX9, OX39. I have found when entering the full post code and house number that the navigation directs you to the wrong house on the street, often by quite a long way, and almost always announces the house to be placed on the wrong side of the road. Wherever odd and even house numbers are on opposite sides of the road the mapping information is inverted. Where the house numbers run sequentially the guidance 99% of the time takes you to the incorrect house.