The Profile Board Method
  
   
     
  commonly used setting out procedure for rural road works is based on the use of a series of profile boards and a string line level, thereby providing control of levels during construction. As a result, the method has become known as the Profile Board Method.

The basic principle when using profile boards is to place a series of level boards that show the exact level 1 metre above the completed construction levels. With practice, this method provides a simple but sound method, providing adequate precision and finally delivers the required quality standards for the completed road construction works.

The method is best described by imagining the excavation of a ditch from point A to point B at the level of the dotted line as shown in the figure below.		  
 
 
  To ensure a correct and uniform level of the ditch, profile boards are placed at positions A and B, with the level boards 1 metre above the level of the excavated ditch.  
   
  Equipment  
 

The Traveller
A third profile board with a fixed height is useful for controlling excavated levels between the adjustable profile boards. It is known as the travelling profile or traveller. During excavation along the line, from points A to B, the traveller can be used to control that the correct levels have been achieved. By placing the traveller in the sight line between A and B, it is easy to determine whether the excavation has been carried out to correct levels. If the top of the traveller is below the sight line between the two fixed profile boards, the ditch has been excavated to a too low level. If the traveller sticks up above the sight line the ditch needs to be dug deeper.

  
   
  To provide good guidance, it is therefore useful to dig slots at regular intervals of 4 to 5 metres along the sight line.  
   
  When sufficient slots have been dug, the workers can start excavating the ditch by joining up the excavated slots. The traveller is then used once again to control that the finished work is to the correct level and that there are no high or low spots.  
  The Line Level  
  The level of each of the profile boards can be controlled by using a line level. The line level is a short spirit level, (about 100 mm long) with a hook at each end to hang it from a nylon string.  
  This instrument needs two persons to operate - one at the end of the line and the second to watch the spirit level. The line operator moves the string up or down until the bubble is centred in the middle between the spirit level marks. The string line will then indicate a horisontal line.  
  The line level can be used to:  
 
  • transfer the exact level of one profile board to another, thereby ensuring that both profiles are at the same level,
  • measure up or down from the horiontal level shown, and set another profile board so that there is a certain difference of level between the two profiles, and
  • measure the slope between two fixed profile boards, and determine which one is higher.
  
  Points to Remember when Using a Line Level  
 
  • The string should preferably be of thin nylon fishing line, allowing for the line level to easily slide along the string,
  • the line must be placed half-way between the two ranging rods - use a measuring tape to establish the exact middle point,
  • keep the string tight - do not let it sag,
  • the line level is a delicate instrument, look after it - do not throw it around and treat it roughly, and
  • check the accuracy of the line level regularly.
  
  Checking the Line Level  
  Take two ranging rods across the road and transfer a level from one rod to the other. Mark the level on the second rod. Keeping the string in the same position on the first rod, take the line level and turn it around on the string. Adjust the string on the second rod until the bubble is in the middle again and mark the new level. Check to see if the two marks are at the same place. If not, measure the difference between the two marks. If the difference between the two marks is less than 10 cm, you can get the right level by taking the point half way between the two marks. If the difference is greater than 10 cm you should replace the line level for an accurate one. It is always a good idea to turn the line level around every time you use it and take the middle of the two marks as the horisontal level.  
   
  The line level has a range of up to about 50 metres. It is easy to carry around and with care can be used for setting out levels and slopes not less than 1 in 300.  
  The Profile Board  
  The other requirement of the profile method is the use of adjustable profiles that can be moved and locked in the desired position. A long lasting profile board is made from thin steel plate which is welded to a short length of metal tubing that can slide up and down and be clamped to a metal ranging rod. A useful size for the metal profile boards has been found to be 40 cm by 10 cm, painted red to make them easy to be seen. Ranging rods are made of hollow metal tubes, often 12.5 mm diameter galvanised water pipe, with a pointed end of sharpened reinforcement steel. They are painted red and white to make them easy to see during setting out.