OmniGraffle comes with a set of data variables that have various levels of dynamicity. (That word works, right? Good.) They change based on each page or canvas number, what you’ve titled the canvas, a line’s length — things like that. And! Couple these variables with a shared layer to pull off headers and footers for each canvas, page, or layer.

1. Create a new shared layer—each object or bit of text you’d like shared with other canvases should be here.
2. Add text to your layer or add text to an object in the layer; select Edit->Insert Variable->Page Number (or whatever!).
3. If you’re just starting your Graffle, use Duplicate to add more canvases that include the Shared Layer. If you’ve already finished and found this searching for a fast way to create headers(!), drag the Shared Layer to each canvas you’d like to add it to.

That’s it! Easy, flexible, and ready to save you some time.