The Degree of accuracy needed in estimating
Accuracy in estimate is very important, if estimate is exceeded it becomes a very difficult problem for engineers to explain, to account for and arrange for additional money. Inaccuracy in preparing estimate, omission of items, changes in designs, improper rates, etc, are the reasons for exceeding the estimate, though increase in the rates is one of the main reasons.
In framing a correct estimate, care should be taken to find out the dimensions of all the items correctly, and to avoid omissions of any kind of work or part. The rate of each item should also be reasonable and workable. The rates in the estimate provide for the complete work, which consist of the cost of materials, cost of transport, cost of scaffolding, cost of tools and plants, cost of water, taxes, establishment and supervision cost, reasonable profit of contractor, etc.
The accuracy, to be observed in preparing an estimate depends on the rates of the item and unit of payment. The higher the rates the greater should be the accuracy with which the quantities are calculated. Where rates are high and paid per unit dimensions should be absolutely correct, though taking dimensions to the nearest 1 cm to 0.5 cm may be allowed for practical purposes. The quantities in such cases should be worked out to at least two places of decimal. But where rates are low and paid for % to % unit such extreme accuracy is not required.
In the case of wall where masonry is paid in cubic meter a few centimeter added to or subtracted from or height would but little affect the total content. But the width or thickness of the wall, where every half centimeter or quarter centimeter affects the results considerably should be taken out with great accuracy. The quantities may be computed to the nearest two places of decimal.
In general, dimensions should be measured to the nearest 1 cm, areas should be worked out to the nearest 0.01 square meters and cubic contents should be worked out to the nearest to 0.01 cubic meter. Thickness of slabs, partitions, etc and sections of columns, pillars, beams, etc should be taken to the nearest half centimeter (0.005 m).
Accuracy in estimate is very important, if estimate is exceeded it becomes a very difficult problem for engineers to explain, to account for and arrange for additional money. Inaccuracy in preparing estimate, omission of items, changes in designs, improper rates, etc, are the reasons for exceeding the estimate, though increase in the rates is one of the main reasons.
In framing a correct estimate, care should be taken to find out the dimensions of all the items correctly, and to avoid omissions of any kind of work or part. The rate of each item should also be reasonable and workable. The rates in the estimate provide for the complete work, which consist of the cost of materials, cost of transport, cost of scaffolding, cost of tools and plants, cost of water, taxes, establishment and supervision cost, reasonable profit of contractor, etc.
The accuracy, to be observed in preparing an estimate depends on the rates of the item and unit of payment. The higher the rates the greater should be the accuracy with which the quantities are calculated. Where rates are high and paid per unit dimensions should be absolutely correct, though taking dimensions to the nearest 1 cm to 0.5 cm may be allowed for practical purposes. The quantities in such cases should be worked out to at least two places of decimal. But where rates are low and paid for % to % unit such extreme accuracy is not required.
In the case of wall where masonry is paid in cubic meter a few centimeter added to or subtracted from or height would but little affect the total content. But the width or thickness of the wall, where every half centimeter or quarter centimeter affects the results considerably should be taken out with great accuracy. The quantities may be computed to the nearest two places of decimal.
In general, dimensions should be measured to the nearest 1 cm, areas should be worked out to the nearest 0.01 square meters and cubic contents should be worked out to the nearest to 0.01 cubic meter. Thickness of slabs, partitions, etc and sections of columns, pillars, beams, etc should be taken to the nearest half centimeter (0.005 m).
