Principles of Measurement

The cost of construction work consists of five discrete but related elements, i.e. labour, equipment, materials, overhead and profit. The general purpose of quantification is to present these elements separately or jointly in such a way that their individual or combined costs can be predicted and later confirmed. In this connection, help from readily available and well-established analysis of rates (pricing process) for a large number of items (Standard Data) can be availed. In addition, the following general principles of measurement are articulated for the benefit of estimators in the offices of both designers and contractors. 

Accuracy 

All work should be measured as accurately as the data will permit. Estimators are always forced with the necessity of having to make decisions about the probable conditions under which work will be done. If measurements can be put onto the firmest base possible, then the approximations and judgement that inevitably have to be incorporated into the pricing process will be minimised. Furthermore, in the event of  a subsequent dispute about the quantity or cost of any item or unit of work, it should be relatively easy to remeasure the quantity to confirm the original estimate. 

Economy 

The estimator should strive to have the least number of words in descriptions of measured items, the least number of extensions and totals. A deliberate policy should be adopted to make the estimate as lean and tight as is practical consistent with the maintenance of verbal and mathematical logic. There are two good 

reasons for the foregoing recommendation : 

1.  Every word is capable of correct or incorrect interpretation, and every calculation may be correctly or incorrectly done; therefore, the less said and calculated the better 
2. As time is always a pressing problem in estimating, methodology that will hasten the process while improving comprehension and accuracy is to be encouraged. 

Standards 

Work should always be measured in accordance with some standard method of measurement, either internally established by the individual company or organisation, or externally recommended for use throughout the industry or trade. There are several following good reasons to adopt such a practice : 

1. The work of the estimator will be made more simple, more rapid and probably more dependable 
2. Communications between the concerned personnel will be clarified, strengthened and hastened 
3. In case of a dispute, there will be precedents on which the estimator can rely. 

In general, the methods of measurements, are based on recommendations contained in various parts of IS : 1200 - 1974 (Methods of Measurement of Buildings and Civil Engineering Works) published by the BIS, New Delhi. 

Confidence 

One of the prime concerns of any estimator is to develop confidence in his or her own work by adopting practices that will assist in avoiding estimating error wherever possible, and to reduce the effects of errors of measurements (or pricing) that accidentally be incorporated into the estimate. One way of minimising the chances of error in measurement is to adopt the practice of measuring overall and deductions and wants. By definition overall means from end to end, or to the fullest extent possible. A void indicates an adjustment made where one item displaces another item, such as at window space in a wall. A 'want' indicates an adjustment made to compensate for deliberate over-measurement, such as at a recess at edges or comers of a wall or slab. 

Overall measurement has a number of following advantages : 

1. Overall dimensions and the location of voids and wants are or should always be overtly stated or clearly implied by the drawings and specifications, and there is therefore, seldom any need for the estimator to calculate or otherwise establish such data, by scaling or other means, and 
2. By measuring the overall first and making deductions second, the effects of any minor errors or oversights in voids or wants will be minirnised. The result may be a minor over-measurement or overpricing, but this is seldom detrimental to the budget. 

Flexibility 

As a general rule, it is better to measure a few more items rather than a few less. The time taken to do the actual measurements will be the same, but there are a number of benefits to be considered. First, wherever a choice can be made between measuring items of work of similar type together or separately, they are best kept initially separate. Although it is relatively easy subsequently to combine subtotals of quantities of similar items or identical prices, it is more difficult to separate and price composite items later.  Second, care should be taken to organise the measurement of work in such a way that the labour, material and equipment components of items can be priced separately or together, depending on what is more expedient. For example, in a reinforced concrete framed buildings, depending on level of quality required, concrete in foundations,  beams, columns or slabs need to be separated out for quantification.  Although the quality (and even the quantity) of concrete might be the same for all these items, the nature of work robe done is different. Even though the work in all four items may be measured in the same measurement unit (cubic metres in this case), the unit price to be subsequently applied to each of the quantities may be different. The quality of concrete in each item may be same or different, and the waste factors may vary from item to item. The labour crew size, type and productivity may be the same or different for each item, as may be the equipment also. 

Simplicity 

It is good to  design and construct buildings using standard and typical components and details wherever possible. However, it is not always possible to stick to such standards, and occasionally some non-typical work will be encountered. To keep the idea of simplicity in measurement, one might say that non-standard and non-typical  work should be measured and kept separate from standard or typical work, so that the additional costs associated with the non-standard aspects of the work can be separately calculated and added on to the costs of the standard work. This technique is called extra-over technique. The following examples will  illustrate this technique. 

1. when measuring drain pipe around a building, the work is measured as if the lines were straight, and the quantity is stated in linear metres, measured along the centre line of the drain. The additional work involved in installing bends, elbows, clean outs and such specials is then separately stated as numbered items, which are later priced on the basis of extra cost of supplying and installing such additional items over the costs of supplying and installing the regular straight pipe. 
2. When measuring a concrete retaining wall built to a batter, that is with one face vertical and the opposite face inclined slightly from the vertical, it is simple to measure the wall as if both faces were vertical and parallel to each other, which is typical, standard or normal configuration for a concrete wall. The area of the sloped portion of the wall is then measured separately and the additional cost of modifying all the accessories and labour to produce that particular feature are calculated and applied to the non-typical quantity as measured. 
3. When measuring centering for a circular column, it is simple to measure it as if it is a square column of side equal to the diameter of the circular column. The extra cost of making a curved surface is treated as a non-typical quantity and separately provided for. 

The primary benefit of this technique is that any discrepancy in the pricing of such non-typical or irregular items is contained within the difference in cost between the standard work and non-standard work, and almost always has to be added to the cost of standard work. A secondary benefit is that the estimator does not usually have to make deductions in his measurements of the standard work, but can simply make a note to add an item for the non-standard portion. A third benefit is that the extent of the additional cost can be identified for study, to assist in determining whether the non-standard feature should be retained, modified or deleted during the design or building process. 

Repetition 

Work should be measured in such a way as to minimise repetition of words or figures. If, for example, a number of floor areas are found to have a common length but varying widths, it is probable that the widths can be totaled or summed and the sum then multiplied once by the common length to produce the required gross area. 

Wherever possible, work should be measured using dimensions that can be used more than once. Such dimensions are often called reflected dimensions and they have two primary advantages. First, if they were correct for the first use, they will be correct for all subsequent uses with appropriate modification where necessary, and second, they eliminate subsequent calculations, thus saving time and reducing possibility of error. Some examples of reflected dimensions are to be found in the area of formwork necessary to form an area of concrete wall, the area of plastering which require to be subsequently painted or the area of flooring concrete which require to be subsequently provided with mosaic tiles. 

Style 

There are a number of useful exhortations to be made under the general title or style. First, estimating work should be done using standard formats. Preferably printed sheets with columns marked in vertical lines should be used. Other related requirements are adequate space to lay-wt sheets of drawings on desks as well as space to layout pencils, scales, calculators, books, and other useful pieces of office equipment or documentation. It is advisable to complete most of the measurement process before the calculation process is started. The estimator should resist the temptation to manually do extension and summary calculations immediately following the establishment of dimensions for each item of work, except where absolutely necessary or logical with respect to other parts of measurements, such as in the use of reflected dimensions. The reason for this'advice is to try to avoid interruptions to the train of measurement thought, to avoid omissions, duplication, or other errors that such interruption can cause. With the use of electronic equipment, such as desktop computers and printers, such advice may not now apply. Typical examples presented in Unit 6 demonstrate acceptable styles for presentation of estimating data.