project.  An   estimator   is  one  who  evaluates  the requirements  of  a  construction  task  and  determines  the quantities of materials needed to accomplish that task As an EA2, you maybe called upon to assist in preparing material estimates, especially for bulk materials, such as fill  materials,  concrete,  and  asphaltic  paving  materials. To be a good  estimator,  you  must  have  sound  and thorough  construction  knowledge  and  experience,  and you must be familiar with the techniques and pitfalls of material estimating. It is beyond the scope of this book to give you the construction knowledge and experience you will need; however, this section does introduce you to some of the techniques and pitfalls that you will use or  encounter  when  estimating  material  requirements. USE OF DRAWINGS AND SPECIFICATIONS Construction  drawings  are  the  main  basis  for defining   required   construction   activities   and   for measuring quantities of material. Accurate estimating requires  a  thorough  examination  of  the  drawings.  All notes  and  references  should  be  read  carefully,  and  all details and reference drawings should be examined. The orientation  of  sectional  views  should  be  checked carefully. Dimensions shown on drawings or computed figures  shown  from  those  drawings  should  be  used  in preference to those obtained by scaling distances. An overall  dimension  shown  on  a  drawing  should  be checked to see if it tallies with the sum of the partial lengths. If scaling is unavoidable, the graphic scale must be checked for possible expansion or shrinkage at a rate different  from  that  of  other  parts  of  the  drawing.  The revision  block  should  be  checked  for  changes  made  to the drawings. The construction plan, the specification, and the drawing must be verified to see if they are, in fact, all talking about the same project. When there are inconsistencies  between  general  drawings  and  details, details should be followed unless they are obviously wrong.   When   there   are   inconsistencies   between drawings  and  specifications,  the  specifications  should be followed. The estimator must first study the specifications and then  use  them  with  the  drawings  when  preparing quantity  estimates.  The  estimator  should  become thoroughly familiar with all the requirements stated in the specifications. Most estimators will have to read the specifications more than once to fix these requirements in  their  minds.  If  the  estimator  makes  notes  while reading the specifications, these notes will prove helpful when the drawings are examined. In the notes, the estimator should list items of work or materials that are unusual or unfamilar. These notes should also contain reminders for use during examination of the drawings. A list of activities and materials that are described or mentioned  in  the  specifications  will  be  helpful  in checking  quantity  estimates. The Seabee Planner's and Estimator Handbook, NAVFAC P-405, is a publication that has been prepared specifically   for   the   Seabee   estimator.   Whenever possible, the tables and the diagrams contained in the P-405 are based on the Seabees’ experience. Where suitable information was not available, construction experience was adjusted to represent production under the  range  of  conditions  encountered  in  Seabee construction. Using the P-405 will save you time in preparing estimates and, when understood and used properly,  will  give  accurate  results. Need for Accuracy Quantity estimates are used as a basis for purchasing materials,   for   determining   equipment,   and   for determining manpower requirements. They are also used in scheduling material deliveries, equipment, and manpower.  Because  of  this  widespread  use,  accuracy  in preparing   quantity   estimates   is   very   important, especially since an error in quantity tends to multiply itself;  for  example,  consider  that  a  certain  concrete  slab is to measure 100 feet by 800 feet. If the estimator misreads the dimension for the 800-foot side as 300 feet, the computed area of the slab will be 30,000 square feet, when it should actually be 80,000 square feet. Since this area will be the basis for ordering materials, there will be  a  shortage  of  concrete  ingredients,  lumber, reinforcing  materials,  and  everything  else  involved  in mixing   and   pouring   the   concrete.   This   includes equipment  time,  manpower,  and  man-hours. Checking  Estimates Quantity estimates should be checked in a manner that will eliminate as many errors as possible. One of the best ways to check your quantity estimate is to have another person make an independent estimate and then to  compare  the  two  estimates  after  both  are  completed. Any  differences  should  be  checked  to  see  which estimate is right. A less effective way of checking is for another person to take your quantity estimate and check all   measurements,   recordings,   computations, extensions, and copy work. 5-5