Expression syntax to get value from other frame?

I think the title says it all. Are there expression statements that allow you to get the value of say angle of x rotation or x position from another object say 30 frames earlier? I have not found a good reference to expression syntax anywhere and what is in the tool manual for the custom tool doesn't seem to have anything like this described.
Thanks.

You need the GetValue() method:

CC1:GetValue("Gamma", 10)

The method acts on the node before the colon. The first argument is an Input on that node, and the second is the frame from which to sample. You can get a frame relative to the current one using the time variable:

CC1:GetValue("Gamma", time-30)

There are lot of useful pointers on the archived VFXPedia:
https://www.steakunderwater.com/VFXPedi ... xpressions

I haven't thoroughly read through the official scripting manual yet, but I suspect a lot of that information is also available there.
http://documents.blackmagicdesign.com/F ... _Guide.pdf

Thanks so much. I'll play with that a while!