We are looking for an answer to this question as well. This is very difficult, and most likely a question for a master carpenter, or perhaps a Geometry professor? Any mathematical geniuses out there? Who can teach us angles: A squared + B squared = C squared, and how to physically adjust an A-Frame to fit these mathematical parameters.
We have built the A-frame with a plum bob, and it works GREAT!, if you don't live in windy Wyoming. Sure, one choice is to wait for a non-windy day, and another option is to wait until midnight, when the wind has died. Let's not stop there! We can get friends out who are willing to hold up plywood all day, against the prevailing wind, and the plum bob must surely be fine, but we are not on the plains, we are working in a valley at the base of the Wind River Range, and a funnel effect nails us from the occasionally, prevailing South-Eastern winds. Of course, this happens when our plywood holders, and the plum bob least expect it; right when we start laying out contours. Days now, we have tried to deal with this Wyoming wind. No contour success.
To be positive and realistic, we are very patient, and hard working, so we can continue on this path of one contour of 700 feet marked in a weekend. However, we are going to find a solution to making the spirit level, A-Frame combo happen, on account of the many acres we are going to swale. This is not only our property we are considering. Other interested parties in our area look forward to participating in these practices, and the winds of Wyoming will continue to slow our momentum.
No matter how this forum turns out, or how the many conversations with local professionals in our area go, we will be diligent in finding a solution to our problem, and will most definitely share our findings with the permies at large. We would like to keep in mind that it is ideal if this design is near free, and can be built with an individual that has a few basic carpenter's tools, and a little such experience. Does that not describe everything that we are trying to do here?
Thanks for any help!
Kyle and Erin