Cost Data

 To enable the estimator to arrive at the reliable unit rates to be used in approximate estimating it is necessary for the site supervisors to keep cost data sheets on the work site on construction operation (during execution of a project) detailing total cost of materials, labour, equipment etc. The resultant unit cost per structure is then worked out. In addition to being useful in checking the actual cost vis-a-vis cost estimated at the starting of the project this unit rate also serves as the basis of preparing an approximate estimation of a similar project in future. It is however, essentially for an estimator to take into account. 

1. variations in the prices of materials, labour and equipment that might have taken place since the completion of the project forming the basis of unit rate, 
2. difference in the site conditions, design methods, materials, method of construction etc for the new structure, and 
3. possibility of variations in the labour and equipment outputs likely to occur due to change in conditions and place when new structure will be constructed. Reliability of the approximate estimate depends on 

• accuracy of cost data maintained, and 
• price adjustments  done to account for the change in the conditions mentioned above.