TRIMMEAN returns the mean of the interior of a data set. @ref is the list of numbers whose mean you want to calculate and @fraction is the fraction of the data set excluded from the mean. For example, if @fraction=0.2 and the data set contains 40 numbers, 8 numbers are trimmed from the data set (40 x 0.2), 4 from the top and 4 from the bottom of the set.
This function is Excel compatible.