I got some rebar and used them as "stakes" for where my building will
be. I stretched a string between each one. To measure the difference in
level of the ground, how do I put up the string? I mean, do I put one
end on the ground and the other at level? What I am having trouble with
is I can get the line level in the center, but if I slide it ot eiher
end the bubble is off.

Does any of this make any sense? What I am trying to do is determine
how "off" my ground is from being level.