# 5.298 Retain two significant figures

### Retain two valid numbers how to retain

Retain two valid numbers how to retain the following:

From the left side of the first non-zero number to start counting the number of two, the excess part of the rounding.

Reading of valid numbers: from the left side of the first non-zero number to start counting until the last digit, a total of a few numbers, is a few valid numbers.

For example, 0.001, the first non-zero number for 1, 1 of the back of no numbers, only a valid number; 0.1000, the first non-zero number for 1, 1 of the back of the three numbers, a total of 5 valid numbers; 5.020, the first non-zero number for 5, 5 of the back of the three numbers, a total of 4 valid numbers.

In fact, this is only our traditional sense has always done so, from middle school to after, but in fact, this error is also very large. However, our normal daily learning life this concept is perfectly fine. A lot of times, when we hand in forms to count something, we ask you to keep a few decimals accordingly.

The method of retaining two valid numbers:

If you calculate the answer to the number of 1, then retain two valid numbers you have to fill in 1.0, because 1 is a valid number, 1.0 is two valid numbers; if you calculate the answer to the number of 1.21, then retain two valid numbers you have to fill in 1.2, because 1.21 is a three valid numbers.

To summarize, to retain two valid numbers is to start counting from the first non-zero number on the left side, and there are two numbers in total, so that is to retain two valid numbers.

Rounding rules for retaining valid numbers:

1, when retaining n valid numbers, if the n + 1 digit ≤ 4 on the rounding.

2, when retaining n valid digits, if the n + 1 digit ≥ 6, then the nth digit into 1.

3, when retaining n valid digits, if the n + 1 digit = 5 and the number behind the number of 0, then the nth digit if the number is an even number will be rounded off the back of the number, if the nth digit of the number is an odd number of times plus 1; if the n + 1 digit = 5 and the back of the number of any number is not 0 If the n+1th digit = 5 and there is any digit that is not 0 after it, 1 is added regardless of whether the nth digit is odd or even.

### How to retain two valid numbers?

Refer to the following method to set up retention:

Tools: computer, Excel

1, first of all, as shown in the figure below, the data, there are a lot of decimal places.

2, and then select the data, click the right mouse button, in the options, select “set the unit format”.

3, in the cell format will be “categorized” under the “General” mode to “numerical value”, after the decimal point to retain the last two.

4, and then click OK.

5, and finally the following chart all the data to retain two valid numbers.

### How to keep two valid numbers?

Retain two valid numbers, the first number that is not 0 starts to take two, this is the practice for decimals where the integer is not 0. When the integer is 0, it is different. For example:0.0123,retain two decimal, then 0.01.

Rounding rules for valid numbers:

1, when retaining n valid numbers, if the n+1th digit ≤ 4 is rounded off.

2, when retaining n valid numbers, if the n + 1 digit ≥ 6, then the nth digit into 1.

3, when retaining n valid numbers, if the n + 1 digit = 5 and the number of digits behind the 0, then the nth digit if the number is an even number will be rounded off the back of the number, if the nth digit is an odd number of digits plus 1; if the n + 1 digit = 5 and the back of the number of digits behind any number is not 0, regardless of the nth digit of the number of digits behind the number of digits behind the number of digits behind the number of digits.

Specifically, the effective number is the number that can actually be measured in the analytical work. What can be measured is the number that includes the last estimated, uncertain digit. We call the exact number obtained by direct reading reliable; the part of the number obtained by estimation is called doubtful. The whole number of digits with one doubtful digit that reflect the size of the measurement is called a valid number. The length of an object is measured to be 5.15 cm. When recording the data, the digit that corresponds to the true value of the data and the experimental result is the significant digit.

Also in math, a significant digit is the number of digits in a number from the first non-zero digit to the last digit of the number, for example, 0.618 has three significant digits, 6, 1, and 8.

Significant digits are approximate rules that roughly maintain significance throughout the entire process of computation. More complex scientific rules are known as propagation of uncertainty.

Numbers are often rounded to avoid reporting insignificant numbers. For example, if a scale measures only to the nearest gram and reads 12.345 kilograms (with five significant figures), it will produce a measurement error of 12.34500 kilograms (with seven significant figures). Numbers can also be simplistic rather than indicative of the precision of a given measurement, for example, to make them faster to pronounce in a news broadcast.

### What does it mean that the result retains 2 significant digits

From the first non-zero digit on the left side of a number to the last digit, all digits are significant digits for that number. For example, 0.025 has two significant digits (2, 5). You can approximate a number by the number of significant digits required. If 2 significant digits are retained, 1.804 ≈ 1.8

### How to keep two valid numbers?

Two valid digits means to keep two digits from the front to the back, in short, just keep two digits.