The dropping of the excess digits in any number is being carried out by rounding off numbers to the appropriate significant figures. The rules for rounding off numbers are as follows:
• The preceding digit is raised by 1 if the last insignificant digit to be dropped is more than 5 and left unchanged if the latter is less than 5. For example (i) 4.796 becomes 4.80 (ii) 8.512 becomes 8.51.
• If the digit to be dropped is 5, the preceding digit should be nearest even number.