Let me give you a quick and cheap suggestion on how to set up the "box" lines at your local contest.  Go to your local hardware or lumber yard and buy three yard sticks.  Now I know that not all of us have struggled through a Trigonometry class, but for those that have, you'll understand what I'm about to say.  Let's say that you're ready to lay out the box lines on your field.  You have already marked a line parallel to the runway and a box where the pilot should stand.  Lay one yard stick on the flight line with one end of the stick at the center of the pilots box (or at the point where the two 60deg lines will join).  This will be called the base line yard stick. Take another yard stick and place one end of it on the end of the first yard stick at the center of the pilot's box and at an approximate 30 deg angle from the first yard stick.

Now, for those that mastered Trig, you remember that the SIN of 30 deg is 0.5.  That means that the perpendicular is ½ of the hypotenuse.  So if you take the third yard stick and place it at the farthest end of the first yard stick, at a 90 deg angle (or perpendicular to the first yard stick), you will have established a triangle, often called a right triangle, because one corner is 90 deg.  If you adjust the far end of the second yard stick to place it at the 18 inch mark, you will have a 30 deg angle between the first base line yard stick and the second one, which forms the hypotenuse.  Now the compliment of 30 deg. is 60 deg., which is exactly what we need to make our first "box" line on the field.  You can now repeat this process in the other direction for the second line, and you will have an accurate 120 deg. box.  If you take a little time and care with the yard sticks, you will have a VERY accurate layout of the field.  Have fun!