One of those "eeesh!" moments arrived today. I read an article in a magazine that included some moving average and seasonality calculations. I was interested in working on the data and set up a spreadsheet to replicate the work I had found. I am pretty sure I found a simple but important mistake in the results in the article so I wrote to the author with all due deference to suggest that there may be a mistake in his article or there may be something I didn't follow but I said I think you might check your work. The author wrote back as follows: All the calculations were carried out using an Excel worksheet. I'm fairly confident they are OK but there may be some rounding errors. Astonishing reply in my opinion. I said to him that there were rounding errors in his work, that was obvious but not important; and I pointed out where there is likely to be an error; but to suggest that because the work had been done on an Excel spreadsheet and therefore he is "fairly confident" that it's all OK was a surprise from one so exalted ... not galvanised into checking it to dispel all doubt! DW