Topographic Abney level

I have used these a few times, and what they lack in accuracy they much more than make up for in portability. There is a small spirit level attached to the protractor and a split mirror in the telescope part so you can see the level bubble as you take your sightings. One method of using them is to sight on something about the same height as your eye above ground (your rodman's eyeball when he is at least a hundred feet away) then set the protractor so the bubble is level while sighting. This is not as easy as it sounds at first because of all the shaking and running back and forth in the vial the bubble does. That lets you measure and record how steep the grade is.
They are OK for rough work and fit in a pocket easily.

Topographic Abney level - photo