Although there are internationally accepted standards around the world government and academic meteorological organisations all have their own specifications for the accuracy, location and reading of weather and climate instruments. Naturally these vary by organisation and the use to which the data is to be put but it would be fair to say that many of these are "scientific research grade" and far from realistic for the vast majority of users. In the UK the Met Office provide information on what they consider to be scientifically correct specifications, location and methods of reading weather and climate sensors. Click here to find more about this from their web site.