I watched a video on youtube (I lost it) that shows rendering parts of the screen to combine them in a single image. I followed it to the point where I couldn't adjust the dimensions under the "set render border", but in the video he had dimensions and I have nothing.
I need it for 4K and 8K renders (without anti-aliasing), but my laptop can't handle it all at once and I don't have time for a 4 hour waiting so this feature will work perfectly.
I'm using version 2.76 so is it moved to another place or removed. Maybe a bug?