What is the intended difference between objects of class "ts", which must have an attribute called "tsp", and objects with that attribute but not that class? Calling time series oriented functions like time() or window() on vectors of numbers produce the classless objects with the tsp attribute. Should methods for atomic vectors check for the tsp attribute and do special things for it? I was wondering if it was just to be compatible with S or S+, where in ancient (pre-class) times, the ".Tsp" attribute indicated that you were dealing with a time series, just as the presence of of a ".Dim" attribute meant the object was a matrix. Bill Dunlap Spotfire, TIBCO Software wdunlap tibco.com