absolute reference via the unified scale

[tilfischer]

Following the IUPAC recommendations for "The Unified Scale for Referencing in NMR" (see http://dx.doi.org/10.1351/pac200173111795 and https://www2.chem.wisc.edu/~cic/nmr/Guides/Other/Xi_chem_shift_scale.pdf), using internal reference such as TMS for other nuclei than 1H is no longer recommended.

With Chemspectra one can easily reference to any internal standard. Absolute reference following the IUPAC recommendations would be a valuable new feature for Chemspectra.

[tilfischer]

As Chemspectra will be substituted with NMRium, I close this issue and forward this to the NMRium developers.