Missing dataframe in er-knife

Hi,
I was trying to replicate one of your visualization and I got an issue
In er-knife/code.Rmd, there is a dataframe called df.months (row174) that is not defined anywhere else in the code. What is it ?
https://github.com/halhen/viz-pub/blob/master/er-knife/code.Rmd
Sincerely yours,
Bastien