I wrote:
>Then in the explanation file one finds the fields explained

about the explanations for the document:
datafile for methane

However if one looks more closely then this doesn't work out.
That is it is probably field 5, where the values are given. Moreover field 2 and 3 seem to be year and month, but what is field 4 ? The numbers are not strictly ascending.

I wrote now an email to Dr. Dlugokencky. But I am on the verge of giving up to understand these Hawaian climate infos.