In most of the everyday situations, we do not need to use highly sensitive measuring devices (instruments). the accuracy of our measurement depends on the purpose for which we use the information.
Example: Suppose someone uses a compass as a guide in going from one end of the school to the other. It would not be a serious error if he/ she is 1o off course. However, 1o off course on a journey to the moon will mean an error of 644000 km.
Besides the error arising from the use of different instrument/ devices, the person taking the measurement is another source of error. For example, in school/ college athletics meet, there are usually two or more time-keepers for the first placing of a (say) 100-meter race, and time-keepers may have slightly different time on their devices (such as sports watch). Therefore, all physical measurements such as mass, length, time, volume and area can never be absolutely accurate. The accuracy depends on the degree of the measuring device (instrument) and the person recording (taking) the measurement. Both of them can never be absolutely accurate.
Rules for Rounding off Numbers
Rule 1: Determine what your rounding digit is and look at the digit to the right of it. If the number is 1, 2, 3, or 4, simply drop all digits to the right of rounding digit. For example,
5.432 may be rounded off to 5.42 nearest to the hundredths place.
5.432 may be rounded off to 5.4 nearest to the tenths place.
5.432 may be rounded off to 5 nearest to units place.
Rule 2: Determine what your rounding digit is and look at the digit to the right of it. If the number is 5, 6, 7, 8 or 9 add one to the rounding digit and drop all digit to the right of rounding digits. For example,
3.786 may be rounded off to 3.79 nearest to the hundredths place.
3.786 may be rounded off to 3.8 nearest to the tenths place.
3.876 may be rounded off to 3.9 nearest to units place.