If not otherwise specified, refer to the centerline of the track for measurements such as curve radius.

**Curve Radius:** To measure the radius of a curve, start at one end of the curve. Then use a square to determine a perpendicular line to the tangent of the curve. Now extend that line out much further using a string, and keep that string perpendicular to the tangent of the curve. Stake the string into the ground so it doesn’t move and stays taught.

Do the same for the other end of the curve you are measuring.

Where your two strings intersect is the center point of the curve. Now measure from the center point to the centerline of your track. This called the curve radius. If your curve has a smooth, uniform curvature, the radius will be the same distance all the way around your curve. It should be at least 30 feet.

**Grade or Slope: **To determine the grade of a stretch of ground or bridge, use an 8’ board that is not bowed (or other straight-edged instrument). Lay the board on the path of the track and determine which end is lowest by visual inspection. Lift the lower end of the board until it is level. Perhaps it may be necessary to anchor a stake to the board to hold it level. Now measure from the ground to the bottom of the lifted end. Divide that number (in inches) by the length of the board (in inches). For example, if the board’s lower end is lifted off the ground by 2 inches, and your board is 96 inches (8’), then your grade is 2 ÷ 96 = 0.0208, or 2%. Grades larger than 2% are discouraged. Consider using bridges/trestles, or digging out the ground more to give the track less slope.