GB/T 8170-2008Rules of rounding off for numerical values & expression and judgement of limiting values (English PDF)

2.1 rounding off for numerical values

The process of omitting the last several digits of the original numerical value and then adjusting the last reserved digit to make the final obtained value approximately equal to the original numerical value.

2.2 rounding interval

The minimum numerical value unit of the rounding value.

2.3 limiting values

The boundary values of the index values which are presented in number, in compliance with the standard (or other technical specifications) and has to be assessed as required by the standard (or other technical specifications).

3.1 Determination of rounding interval

3.2 Rules of rounding off

3.2.1

The numerical value is rounded down if the leftmost one of the numbers intended to be discarded is less than 5; and the reserved numbers keep unchanged.

Example. Round 12.1498 to the single digit, 12 is obtained. Round 12.1498 to one decimal place, then 12.1 is obtained.

3.2.5

When rounding off the negative number, first round its absolute value according to those specified in 3.2.1~3.2.4 and then add the negative sign at the front of the obtained value.

3.3

Continuous rounding off is not permissible

3.3.1

The rounding number shall be obtained by rounding the numerical value only once after the rounding interval or rounding digits are specified. More than one time of continuous rounding off in accordance with 3.2 is not permissible.

(expressed as -0.036 in specified occasions)

4.1 General principles for written limiting values

4.1.1

The limiting value shall be provided for the index or parameter which is presented in numbers and has to be assessed as required in the standard (or other technical specifications).

4.2 Terms expressing the limiting values

4.2.1 Basic terms

4.2.1.1

The basic terms and symbols expressing the limiting values is detailed in Table

1.

4.2.1.2

The basic terms may be used by combination to indicate the scope of limiting value.

4.2.2 Values with limit deviations

4.2.2.1

Basic value A with upper deviation +b1 of absolute limit and lower deviation - b2 of absolute limit refers to the values fromA-b2 to A+b1 meet the requirements and it is expressed as.

4.3

Comparison method of the measured value or its calculated value and the limiting value specified in the standard

4.3.1 General provisions

4.3.1.1

When judging whether the measured value or its calculated value meet the standard requirements of not, the measured value of test or its calculated value shall be compared with the limiting value specified in the standard, and any of the following methods may be adopted for comparison;

4.3.1.3

If one of comparative methods is specified in the standard or relevant document, it shall not be changed once been determined.

4.3.2 Complete numerical comparison method

Do not round off the measured value or calculated value (or even though the value has been rounded off, it shall be indicated that it has been rounded down, up or neither of them) and then compare this value with specified limiting value;

4.3.3 Rounded-off-value comparison method

4.3.3.1

Round off the measured value or its calculated value, and the rounding off digit shall be consistent with the digit of the specified limiting value.

4.3.3.2

Compare the rounded off values and the specified limiting value, if this value exceeds the specified range of limiting value (no matter large or not), it will be judged as do not meet the requirements. See Table 3 for examples.

Table 3 (continued)

4.3.4 Comparison of two kinds of judgment methods