Sky dome rotate

Which friends can explain the role of the addition node here?Many thanks!

Looks like an old setup to me. What you are you trying to achieve? If you want to slowly rotate the Sky dome it may be easier to use a Panner node.

Thank you!Oh yes!You are right!I set it through a toturial,like so stupid,,haha(make a sky dome just rotate it,)

I have a new question~Do not know if you can help me~Q:The landscape grasstype was missed When i render the movie out by squence,but the foliage grass exist,i don’t know what’s wrong about render settings else