Hey, I was just goofing around with some excel reports and noticed a very odd rollup behaviour. I had a point which kept track of hourly temperature data and which I accidentally deleted. To remedy this I went and downloaded daily mean temperatures and loaded them in to the history, so now said point has one entry each day at 17:00. I did this because in future we want to keep using this point, hourly data, and the report will give me an average rollup on a per day basis. To make sure that the average of a single point is calculated correctly I ran a little test excel report. This is where things didn't work quite as expected. I admit this is an oddball case but is there an explanation?
Left column below is the actual raw data and the right column is the daily average I get form the system.