I'm sure many of you knew this but it was new to me and I came across it today, so in an effort to get it out there a bit more, i document it here. It concerns the fact that COUNTIF and SUMIF (and their 2007 plural counterparts SUMIFS and COUNTIFS) carry forward the limitation that Excel has of 15 significant digits. (As does 1-2-3 and OpenOffice) http://support.microsoft.com/kb/269370 I knew this limitation, but didn't realise the two functions concerned followed this limit' I had to...