The level is actually pretty easy to make and can cost you nothing if you have some spare building materials lying around. I used two pieces of 1x2x6' pine to make the legs of the frame. You can tie or nail the pieces together but we opted to use screws and wing nuts so we can take it apart for storage.
So here is a pic showing the frame before we put on the crosspiece.
Next we added the cross piece and again used screws and wing nuts. Hubby was checking to make sure everything was level.
Before we added the plumb bob, which you can buy at your local home improvement store, hubby marked the center of the cross piece. When trying to find your center mark you should place your level somewhere that is as level as possible. Mark where the feet of your level are on the ground and then mark where the string is against the wood. Now flip the frame so the feet are in each others footprints. Mark where the string is again if it is in a different place. The center of these two marks are your level.
We were lucky and the string was in the same place both times. Here is a picture of the plum bob hanging in place.
Next we had to test it of course. It can be a little tedious but you can see in this picture how the line begins to curve. If we were preparing to dig a swale, we would continue to measure the length of the swale and then dig along the line we have marked. You want a swale to be slightly uphill from where you want to hold the water. The bottom of the swale should be level so the water will stay for as long as possible. When you dig, the dirt should be placed on the downhill side of the swale to form a berm to help with water retention.
Not many of us will ever need an A frame level but for anyone who has ever wondered how to make one, there it is! Now I just need some heavy earth moving equipment.