Hello peeps!

I've been browsing around Isodat trying to figure some things out. I came across the Standard Editor and have a few questions.
Who decides the "Value".  For example, one of our "working standards" is "Lab N2 tank". The gas is "N2", Delta is "d15N/14N" and Value is "-0.971". Where did this number come from? 

That same working standard uses the "Air-N2" Primary standard whose "Prim. Std. Ratio" is "0.0036782". Should this number be "0.0036764" which is the R15N/14N of Air? 

Other working standards have similar configurations but have a different value for N2 such that the "d15N/14N" is 0 vs Air-N2, but the primary standard ratio is the same as the "Lab N2 Tank" working standard. 

Any information about this tab would be great since the Isodat manual lacks a little bit.