No disrespect to exmpa but I am pretty certain what Rocketeer has is more like this http://www.laser-measure.co.uk/leica-disto/leica-runner-20-24.html.

What exmpa describes is an instrument which measurers a vertical height, the telescope not only rotates in the horizontal plane by 360* but also in the vertical plane.

As always Wikipedia is your friend http://en.wikipedia.org/wiki/Dumpy_level

Paul