George, Forgive me if I'm preaching to the converted but...
In mathematics, particularly statistics, the term *average* is not used. There are three other measures; mean, median and mode. In most cases, the mean has the same meaning as we normally use for average. i.e. add up all the values and divide by how many values you have. (Alternatively, time how long it takes the earth to get back to the same position in the heavens and divide by the number of days in the year.) If you were to list all the values in ascending order, the median is the value halfway down the list. Exceptional values (large or small) that would automatically influence the mean will not affect the median. (I guess that this would give you a value of day length around the equinoxes.) If you have data that takes one of a number of discrete values (e.g. integers) then you can find the mode. This is the value that occurs most often. (If day length were timed to the nearest minute you could use this measure, but you might well end up with several different daylengths all occuring with the same frequency!) I think this answers your question, even if only in as much as average and mean are usually taken to be the same, at least in statistics! David Higgon London
