Rounding Numbers and Specifications

Automotive inspection, TS 16949, IATF 16949


If I have a data collection form and the data inputs are whole numbers, should the report then use rounded whole numbers rather than to 2 decimals points?  I’d like to be accurate.


It depends on the specification.  If the specification is a whole number, then each reporting value should be in a whole number.  The issue comes in when inspection, measurement, and test equipment (IM&TE) gives a read-out in decimals, as they should.  (remember the requirement that the IM&TE should be more accurate than the desired result).

For example: if the specification is XX, then the test result should be reported in XX.  If the specification is XX.X, then the result should be reported in XX.X (one decimal place).

Not doing so can lead to problems.  If the specification is, for example 8 – 10, then a result of 8, 9 or 10 is passing.  If the IM&TE gives a result of 10.1 and you record 10.1 then you open the door for interpretation by others.  The best thing to do is define the recording of test results in the test procedure / method.

Once when I was being audited, the ISO auditor claimed that the company was accepting out-of-specification test results.  The specification was 0.01 max.  The test instrument gave a digital read out in the 4th decimal place and the technician record all 4.  The test result was 0.0102.  The auditor claimed that was over the max or 0.01. Boy did I have an argument with him (I won).  After that,the technicians were trained to round to the readings and record only to 2 decimal places (i.e. significant digits)  This was also added to the test instruction.

James Werner