NMR spectrum referencing

[schatzsc]

There seems to be only a fixed list of solvents which can be used to reference the NMR spectrum. This is quite extensive, but I
still miss (or did not find) the option to "custom-add" other substances not in the list, for example when you use some secondary internal standard not on the "normal solvent list" or you are not working with 1H (and possibly 13C also) nuclei.

It would be important to be able to

a) add additional reference compounds to the list and
b) change the values if necessary, as some of the values seem to be not those in the famous "NMR shifts paper" by Bercaw et al. Organometallics, 2010, 29, 2176–2179, https://doi.org/10.1021/om100106e