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Tham khảo tài liệu 'project planning control 4 e part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Estimating There are a number of estimating methods in use varying from the very approximate to the very accurate. Most organizations have their own estimating norms developed over the years and updated regularly to reflect changes in operating methods and systems. In addition the variations in labour rates material costs and exchange rates will have to be built into the estimate. The four main types of estimating techniques each giving different degrees of accuracy are 1 Subjective With this method the estimator relies on his experience of similar projects to give a cost indication based largely on very subjective feel or hunch . Geographical and political factors have to be taken into account as well as the more obvious labour and material content. Frequently such estimates are required to be given with little notice so that the accuracy may well be in the order of 40 . Such an approximate method of estimating is therefore often called guesstimating . 2 Parametric By using well-known empirical formulae or ratios in which costs can be related to specific characteristics of known sections or areas of the project it is possible to produce a good estimate on which firm decisions can be based. Clearly such estimates require to be qualified to enable external factors to be separately assessed. For example an architect will be able to give a parametric estimate of a new house once he is given the cube height X length X depth of the proposed building and the standard of construction or finish. The estimate will be in cubic metre of structure. Similarly office blocks are often estimated in square metre of floor space. The qualifications would be the location ground conditions and costs of the land etc. Another example of a parametric estimate is when a structural steel fabricator gives the price of fabrication in ton of steel depending on whether the steel sections are heavy beams and columns or light lattice work. In both cases the estimate may or may not include the .
