project. An estimator is one who evaluates therequirements of a construction task and determines thequantities of materials needed to accomplish that taskAs an EA2, you maybe called upon to assist in preparingmaterial estimates, especially for bulk materials, such asfill materials, concrete, and asphaltic paving materials.To be a good estimator, you must have sound andthorough construction knowledge and experience, andyou must be familiar with the techniques and pitfalls ofmaterial estimating. It is beyond the scope of this bookto give you the construction knowledge and experienceyou will need; however, this section does introduce youto some of the techniques and pitfalls that you will useor encounter when estimating material requirements.USE OF DRAWINGS ANDSPECIFICATIONSConstruction drawings are the main basis fordefining required construction activities and formeasuring quantities of material. Accurate estimatingrequires a thorough examination of the drawings. Allnotes and references should be read carefully, and alldetails and reference drawings should be examined. Theorientation of sectional views should be checkedcarefully. Dimensions shown on drawings or computedfigures shown from those drawings should be used inpreference to those obtained by scaling distances. Anoverall dimension shown on a drawing should bechecked to see if it tallies with the sum of the partiallengths. If scaling is unavoidable, the graphic scale mustbe checked for possible expansion or shrinkage at a ratedifferent from that of other parts of the drawing. Therevision block should be checked for changes made tothe drawings. The construction plan, the specification,and the drawing must be verified to see if they are, infact, all talking about the same project. When there areinconsistencies between general drawings and details,details should be followed unless they are obviouslywrong. When there are inconsistencies betweendrawings and specifications, the specifications shouldbe followed.The estimator must first study the specifications andthen use them with the drawings when preparingquantity estimates. The estimator should becomethoroughly familiar with all the requirements stated inthe specifications. Most estimators will have to read thespecifications more than once to fix these requirementsin their minds. If the estimator makes notes whilereading the specifications, these notes will prove helpfulwhen the drawings are examined. In the notes, theestimator should list items of work or materials that areunusual or unfamilar. These notes should also containreminders for use during examination of the drawings.A list of activities and materials that are described ormentioned in the specifications will be helpful inchecking quantity estimates.The Seabee Planner's and Estimator Handbook,NAVFAC P-405, is a publication that has been preparedspecifically for the Seabee estimator. Wheneverpossible, the tables and the diagrams contained in theP-405 are based on the Seabees’ experience. Wheresuitable information was not available, constructionexperience was adjusted to represent production underthe range of conditions encountered in Seabeeconstruction. Using the P-405 will save you time inpreparing estimates and, when understood and usedproperly, will give accurate results.Need for AccuracyQuantity estimates are used as a basis for purchasingmaterials, for determining equipment, and fordetermining manpower requirements. They are alsoused in scheduling material deliveries, equipment, andmanpower. Because of this widespread use, accuracy inpreparing quantity estimates is very important,especially since an error in quantity tends to multiplyitself; for example, consider that a certain concrete slabis to measure 100 feet by 800 feet. If the estimatormisreads 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 thisarea will be the basis for ordering materials, there willbe a shortage of concrete ingredients, lumber,reinforcing materials, and everything else involved inmixing and pouring the concrete. This includesequipment time, manpower, and man-hours.Checking EstimatesQuantity estimates should be checked in a mannerthat will eliminate as many errors as possible. One ofthe best ways to check your quantity estimate is to haveanother person make an independent estimate and thento compare the two estimates after both are completed.Any differences should be checked to see whichestimate is right. A less effective way of checking is foranother person to take your quantity estimate and checkall measurements, recordings, computations,extensions, and copy work.5-5
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