Figure 5-2.—Foundation plan and detail.Sources of ErrorOmissions are usually the result of carelessFailure to read all the notes on a drawing or failureto examine reference drawings results in manyomissions; for example, an estimator may overlook anote that states “symmetrical about ~’ and thuscompute only half of the required quantity.Errors in scaling obviously mean erroneousquantities. Great care should be taken in scalingdrawings so that correct measurements are recordedSome common scaling errors are using the wrong scaleand failing to note that a detail being scaled is drawn toa scale different from that of the rest of the drawing.Remember that some drawings are not drawn to scale.These, of course, cannot be scaled for dimensions.Sometimes a wrong interpretation of a section of thespecifications can cause errors in the estimate. If theestimator has any doubt concerning the meaning of anyportion of the specification, he should request anexplanation of that portion.examination of the drawings. Thoroughness inexamining drawings and specifications will usuallyeliminate errors of omission. Checklists should be usedto assure that all activities or materials have beenincluded in the estimate. If drawings are revised aftertakeoff, new issues must be compared with the copyused for takeoff and appropriate revisions made in theestimate.Construction materials are subject to waste and lossthrough handling, cutting to fit, theft, normal breakage,and storage loss. Failure to make proper allowance forwaste and loss results in erroneous estimates.Other sources of error are copying errors,inadvertent figure transpositions, and computationaland arithmetic errors.ESTIMATING BULK MATERIALREQUIREMENTSAll material estimates, including those for bulkmaterials, are used as a basis for material procurement5-6
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