Hello,
very noob question, i want to add a value to the value it was last frame. I think it is the ++ kind of operation that namned c++ (?) i am looking for.
Or to put it simpler: If I want a slider (Box, local Y Position, Driver) to control the spin speed of a planet, I can use a code like “frame*pos_y_box/15”. But when i animate the box slider now the spin speed is not changing smoothly, but is jumping wild. Of course because the current frame number is multiplied… So I come back to the first sentence: I need to add the current value to the value of the last frame.
I know this is probably a basic step of programming, noob 
Thanks for help.
Stefan