Do you know about the basic principles of measurements? In this article, you can quickly learn about manual taking off procedure. Firstly, we need some dimensions papers, also called taking off sheets (TDS) to the purpose of taking off.
BS 3327:1970, ‘Specification for Stationery for Quantity Surveying’ specifies the paper size for Dimension Papers as A4 (210 mm X 297 mm) ruled vertically as per the figures are given below. The rulings, widths & purpose of columns on the face and reverse sides of the dimension paper are illustrated in Figures 1 & 2.
Each dimension sheet is split into two identically ruled parts, each consisting of four columns. The 9 mm wide first column of the face side and the last column of the reverse side is the binding margin for binding the dimension papers. The purpose of each column, as indicated below.
- Column 1 is the timesing column where multiplying figures are entered when there are more than one of the particular items being measured.
- Column 2 is the dimension column where the actual dimensions, as scaled or taken direct from drawings, are entered. There may be one, two, or three lines of dimensions in an item depending on whether it is linear, square, or cubic.
- Column 3 is the squaring column where the length, area, or volume obtained by multiplying together the figures in columns 1 & 2 is recorded, ready for transfer to the abstract or bill.
- Column 4 is the description column where the written description of each item is entered. The right-hand side of this wider column is used for preliminary calculations & other information needed in building up the dimensions &references to the location of the work and is referred to as ‘waste’.
Form of Dimensions
There are five forms of dimensions in the principles of measurements as set down by the taker-off. They are as follows:
- Cubic measurements
- Square or superficial measurement
- Linear measurement
- Numbers or enumerated items
Order of Dimensions
A constant order of entering dimensions shall be followed throughout, and it is customary to write down in the dimension column in the same order:
- Horizontal length
- Horizontal width or breadth
- Vertical depth or height
Although the order will not affect the calculations of the cubic or square measurement, it is very valuable in tracing measurements later, and an incorrect order in a description may even sometimes mislead an estimator in pricing. Therefore, the quantity surveyors should care for the order of dimensions in the principles of measurements.
When setting down the dimensions immediately under each other in the dimension column, each separate item is divided from the next by a line.
An item to be enumerated is usually indicated in one of the following ways.
Sometimes, the Standard method of measurements (SMM) requires the insertion of an item, which is a description without a measured quantity and indicated as follows.
There is no need to label the dimensions as cube, square, linear, etc. as if a rule is always made to draw a line under each measurement; It is obvious from the number of entries in the measurement under which category it comes.
Sometimes, when the taker-off has written the dimension it is found that there are several similar items having the same measurements, and to indicate that the measurement is to be multiplied it will be ‘timesed’ thus:
The ‘timesing’ figure is kept in the first column and separated from the dimension by a diagonal stroke. An item ‘timesed’ can be ‘timesed’ again, each multiplier multiplying everything to the right of it, thus:
In repeating a dimension, the taker-off may find that it cannot be multiplied but added. Where additional items occur, the dimensions may be increased by ‘dotting on’ or added, thus:
Measurement of Irregular Figures
Sometimes it is necessary to measure the areas of triangles and circles, the circumferences of circles, and the volume of cylinders, etc. and the usual method of entering the dimensions are as follows:
A bracket is used whenever more than one measurement relates to a description or group of descriptions. The bracket being placed outside of the squaring column, a vertical line with a little cross marks to indicate top and bottom. The total quantity indicated by the measurements within the bracket is set against each related description on the abstract.
Alteration of Dimensions
When dimensions have been set down incorrectly, they shall never be erased or altered. Incorrect dimensions should be canceled by writing NIL in the squaring column alongside the wrong figures and the extent of the cancellation indicated by brackets and arrowheads. The correct dimensions shall then be written clearly in the dimension column, and this can be done thus:
Except in very simple cases, dimensions shall not be calculated mentally. Not only will the risk of error be reduced if the calculations are written down, but another person can readily see the origin of the dimension when they are checked. The preliminary or waste calculations involved in determining the dimensions and any related explanatory comments shall be written clearly on the right-hand side of the description column. The risk of error will then be reduced since these calculations can be checked during working up, and in addition, the process by which the dimensions were determined will be made clear for later reference.
Waste calculations are written to three decimal places, and the results reduced to the nearest 10 mm (i.e., 5mm and above 5 mm as 10 mm and below 5 mm neglected) before transfer to the dimension column.
Spacing Of Dimensions
All measurements and descriptions shall be spaced well apart so that it is quite clear where one begins and it ends. It is not unusual for a taker-off to realize that after writing down the measurements that some item has been overlooked and it is desired to insert it in its proper place. If the dimensions are well spaced out, it can be squeezed in, but otherwise, it will have to be inserted elsewhere and cross-references made, which only complicate the work.
The description of the item measured is set down opposite the measurement in the description column. Descriptions shall be adequate, clear, and concise and built up following the order set out in the tabulated rules of the SMM together with the necessary information from the supplementary rules.
The Ampersand or ‘Anding On’ (&)
When dimensions are to be repeated for other items, this is indicated by the use of the ampersand sign (&), thereby preventing the repetition of dimensions. However, care must be taken when combining linear with superficial items or superficial with cubic items.
Measurements shall always be carried out ‘working from whole to the part,’ i.e., measure overall and then makes any deductions if necessary. Deductions of previously measured quantities are made in the description column, as shown below. The item must be preceded by the word ‘Deduct’ (Ddt) and to ensure that only the intended items are properly deducted the next item shall be preceded by the word ‘Add’ for the avoidance of any doubt.
Headings are essential in taking off in order that the dimension sheets can be identified with a particular contract and also indicate the sequence of measurement for later reference. The title of the contract must appear at the head of each dimension sheet. In contracts with several buildings, the name of the building unit shall be incorporated in the title on the appropriate dimension sheets.
Numbering, in sequence at the bottom of the column, must identify each column of dimensions. This is useful for reference purposes and provides a check, which ensures that the dimensions are complete.
Extra Over Items
Certain items are measured as extra over the item of work in which they occur, in which case the estimator will price the additional cost involved as to some extent this item will have been previously measured. Examples of this type of item are bends on rainwater goods (extra over for pipes), extra over for rock excavation when excavating the soil.
Items that are to appear inset in the bills of quantities, usually described as ‘written short’ are entered in the same manner as other descriptions. This avoids breaking completely the sequence of linear items from superficial items.
Abbreviations & Symbols
Many of the words entered in the description column are abbreviated in order to save space and time in entering the items by highly skilled technical staff. Many abbreviations have become almost standard and are of general application. A considerable number of abbreviations are obtained by merely shortening the particular words.