My word! You can sure make this stuff more complicated than necessary. I am not a rig or pipeline or super talented nuclear process plant welder, but I do know how to build fence. Pull a heavy string line to set your post as you want them. If it's a long straight stretch, set every forth or fifth post and eyeball them against the string. When you have those set, go back and fill in with the remainder of post. Reason being, the post already set will help keep the wind or grass from throwing your line off. Now that your post are set, measure up the post and make a mark at the height your wanting. Tie your string to the first post at that height, and pull to last post. Take thin wire, electrical tape or string and twitch the string line up every other post or so at the marked level your shooting for. Step back and look at it from different places to see where to adjust to make the fence FLOW. If you follow the height from the ground on each post it's going to look like a drunk snake. Or you can try the transit level, but I have built fence on very few completely flat places. Hope this helps. Not trying to get anybodies dander up here, just actually have done this steadily for the last 20 years.