I take your point Wayne and I'm sorry about the thread hijack. Maybe I could have been a bit more explicit because when Martin explained the problem the person on the other end of the phone at Garmin knew which model GPS unit Martin had before Martin had told them. So Garmin are aware that there is an accuracy problem. However, because this Unit is over three years old they weren't prepared to fix or replace it under warranty.
I guess you just pay your money and take your chance but in Martin's case having known him for a long time he has definitely looked after this and all his other mark laying kit.