http://reap-eastafrica.org/blo...
I see it now. You "calibrate" the A-frame to be a level - the feet are at the same contour if the dangling string hangs to the right point on the semi-horizontal cross-bar.
To calibrate the level, set it on pretty level ground and mark lightly where the dangling string intersects the cross-bar.
The flip the A-frame around so the right leg is where the left leg was (and vice-versa). Then note where the dangling crosses the cross-bar now.
Then mark darkly exactly halfway between them. That shows when the feet are level with each other
Then you can "walk" the A-frame horizontally across a contour, like walking a divider across a map, leaving stakes where each foot had to be placed in order to make that foot exactly level with the other foot.
It relies on the ends of the pols not sinking into the soil, so perhaps two little cross-bars as "feet" would be an improvement.
