12 Expression of results
Report the calculated cetane number, rounded to the nearest 0.1. Any CN ending in exactly 5 in the second decimal place shall be rounded to the nearest even 0.1.
NOTE 30 For example, 35.55 and 35.65 should be rounded to 35.6 CN.
13 Precision
13.1 Repeatability
The difference between successive test results, obtained by the same operator with the same apparatus under constant operating conditions on identical test material would, in the normal and correct operation of the test method, exceed the values in table 1 in only one case in twenty.
13.2 Reproducibility
The difference between two single and independent test results, obtained by different operators working in different laboratories on nominally identical test material would, in the normal and correct operation of the test method, exceed the values in table 1 in only one case in twenty.
NOTE 31 Repeatability is based on the ASTM National Exchange Group (NEG) monthly sample testing program data from mid-1978 through 1987. During this period each exchange sample was rated twice on the same day by the same operator on one engine in each of the member laboratories).
Reproducibility is based on the combined NEG monthly sample testing program from mid-1978 through mid-1992, the Institute of Petroleum monthly sample data for 1988 through mid-1992 and the Institut Français du Pétrole monthly sample data for 1989 through early 1992.
The combination of the large number of sample sets and the fact that each sample is tested by 12 to 25 laboratories provides a comprehensive picture of the precision achievable using this test method. Analyzed graphically, the respective sample standard deviations were plotted versus CN. The variation in precision with respect to CN level for these data is best expressed by a linear regression of the values. The average standard deviation for each CN level has been multiplied by 2.772 to obtain the respective repeatability and reproducibility values.
14 Test report
The test report shall contain at least the following information:
a) a reference to this International Standard;
b) all details necessary for the complete identification of the sample tested;
c) the results of the test (see clause 12);
d) any deviation, by agreement or otherwise, from the procedures specified;
e) the date of the test.