[pstricks] Example 15.1.10 from PSTricks Book

[Herbert Voss]

Hernando Diaz wrote:
> Trying to understand example 15.1.10 from Herbert's book, I ran into the
> following error:
> ! Missing number. Treated as zero
> When using month's name as label. The definitions \Monat and \Level work
> fine. Could someone point my errors?
> 
> I am using the online version. 
> Maybe I am missing something, because of the language barrier. My german
> skills range from lousy to nonexisting.
> 
> The code I am using:
> \listfiles
> \documentclass{article}
> \usepackage[latin1]{inputenc}
> \usepackage{pstricks,pst-plot,pstricks-add}

do not load pstricks-add here.

Herbert