This section is from the book "The Building Trades Pocketbook", by International Correspondence Schools. Also available from Amazon: Building Trades Pocketbook: a Handy Manual of reference on Building Construction.
By means of the following table the square, cube, square root, cube root, and reciprocal of any number may be obtained correct always to five significant figures, and in the majority of cases correct to six significant figures.
In any number, the figures beginning with the first digit* at the left and ending with the last digit at the right, are called the significant figures of the number. Thus, the number 405,800 has the four significant figures 4, 0, 5, 8; and the number .000090067 has the five significant figures 9, 0, 0, 6, and 7.
The part of a number consisting of its significant figures is called the significant part of the number. Thus, in the number 28,070, the significant part is 2807; in the number .00812. the significant part is 812; and in the number 170.3, the significant part is 1703.
In speaking of the significant figures or of the significant part of a number, the figures are considered, in their proper order, from the first digit at the left to the last digit at the right, but no attention is paid to the position of the decimal point. Hence, all numbers that differ only in the position of the decimal point have the same significant part. For example, .002103, 21.03, 21,030, and 210,300 have the same significant figures 2,1, 0, and 3, and the same significant part 2103.
The integral part of a number is the part to the left of the decimal point.
It will be more convenient to explain first how to use the table for finding square and cube roots.