I've had good luck using a water level as shown in this Brad Lancaster video http://www.youtube.com/watch?v=pRjNA0DZZb4
. If you pay attention to how you number the sticks as shown in the video, the larger number will be higher. I used a couple of pieces of PVC pipe I already had, and duct taped some yard sticks to them. Just be sure you reference the BOTTOM
of the stick to set the yardsticks or write your numbers.
I then added a small plastic electric fence post http://www.ruralking.com/post-poly-electic-step-in-white.html?utm_medium=google&utm_source=cse&cvsfa=1908&cvsfe=2&cvsfhu=303730303430343433
by duct taping one of the pipes to it with the bottom of the pipe lining up with the bottom of the plastic part. This allows me to use this by myself. Just place the fence post portion where you want to start the countour, then place the other pipe by the first to find your "magic number". I try to put an amount of fluid in the tube so that I don't have to stoop to read it, but make sure you allow enough tube "space" above it so that it isn't forced out when you lift one or the other of the pipes too far. Once your numbers read equally for the calibration your set to go. Just move 2 to 4 feet away on your perceived contour, hold your pole plumb, then move it slightly uphill or downhill until you match your number, set a marker or flag at the base of the pole. Move further away on your contour, find your number by moving uphill or downhill, set marker, repeat. When you near the end of your tubing, just go back and get your staked pole, place it at one of your last flags, then take off again on your contour. The number should stay the same. One advantage of the water level over the A-frame is that you are not locked in to a certain distance from your last point. If you go 4 feet away from your previous point and find an obstacle (say a rock or log) you can just go back a foot or forward a foot to establish your point. The distance between your points is not critical.
One additional point is that any given point
along this contour line might be an anomaly due to being on a "lump" of ground, or in a small depression. You can pay attention to any obvious oddities when you place you pole but don't obsess over it. After you have place 10 to 20 markers, sight back along your contour. You will probably see some "oddball" points, but you will also see a generalized curve developing. This "smoothed" curve is what you're after.
I also allow some of my tubing to extend above the pole. This allows me to fold the tubing over and tightly place a rubber band on it for transporting without spilling the liquid. You can also fold it over and put a rubber band on it loosely to serve as a damping effect so the liquid levels with less dancing. I am now using holding tank antifreeze as my liquid, so I can work in freezing weather, and the slight coloration makes it easier to see.