I'd like to ask if it is now generally accepted practice to normalise the oxygen isotope scale for carbonate analysis by using values for NBS18 and NBS19 of -23.00 and -1.95 per mille (VPDB)? Regards, Steve Crowley Department of Earth & Ocean Sciences University of Liverpool 4 Brownlow Street Liverpool L69 3GP UK 0151 794 5163/5164