# Question #85a3f

##### 1 Answer

Do not round off to the correct number of significant figures until the final calculation.

#### Explanation:

If you round off after each step, you may get accumulated **round-off error**.

Always carry at least one extra digit (called a **guard digit**) to prevent round-off error.

Any intermediate answers that you must report **for grading** should be rounded off to the correct number of significant figures.

If you must use an intermediate answer in a later calculation, use its **unrounded value** (not the rounded value that you reported earlier).

**Example**

**(a)** Rounding off at each step

Calculate the value of

**(b)** Carrying a guard digit

Calculate the value of

If you retain all the digits in your calculator, the answer becomes

**Moral:** Retain one guard digit and **round off only at the end**.