Greetings, I assume this is an easy question but it seems my last math class was a long time ago. Usually I don't care about the exact value of my CO2 ref gas on our gasbench system since everything is normalizied to reference materials with known values (and working gas cancels out). I just type in a value for the working gas in the isodat standard editor which will give a delta value close to the correct value. I need to calculate the CO2 value of the working gas now and my idea was just to caluclate the things backwards. Assuming that my reference material (e.g. NBS19) will produce a CO2 with a known value it should be possible the calculate the delta value of the working gas etiher from the raw delta values or the ratios given in Isodat by treating the ref gas as the sample and the NBS 19 as the standard gas. However, sitting in front of Isodat and the equations it is not so obvious anymore...can anyone point me in the right direction? regards, Robert -- Dr. Robert van Geldern GeoZentrum Nordbayern / Applied Geosciences University of Erlangen-Nuremberg Schlossgarten 5 91054 Erlangen, Germany mailto:[log in to unmask] www.gzn.uni-erlangen.de fon: +49(0)9131-85-24780 (office) fax: +49(0)9131-85-29294 Room: O 0.106 (office)