ISO/IEC JTC1/SC22/WG5 N2112

      WG5 decision on a new work item on a TS on Units of Measure

                      John Reid, 6 July 2016

The UNITS proposal that was brought to WG5 at the meeting in 2013, see
N1969 and N1970, was intended to provide assistance to programmers who 
must manage sets of physical units used in engineering analysis programs.  
It was proposed as a Technical Specification (TS) in recognition of the 
fact that it was too large a feature for the plans that had been agreed 
for the next revision. 

The specific case cited was the loss of a spacecraft that was intended 
to explore Mars.  The basic issue was the use of different sets of units 
(in this case, Imperial versus SI) in different programs run by different 
organizations. This discrepancy was not noticed until too late and 
resulted in the loss of the spacecraft.

While the sequence of events above describes a particular case where a 
units checking package might have assisted with earlier notice of the 
error, and other cases where such a feature would have been useful were 
mentioned, there did not appear to be wide-spread demand for this feature.  
No supplier of compilers reported significant user requests for a 
units package.

The estimates of compiler suppliers of the cost-to-implement this
feature were high. It was felt that implementing a standardized units 
proposal would take resources away from other efforts, including
fixing bugs, improving efficiency, and implementing other features.

Of particular concern was the long delay between the adoption of the
Fortran 2003 standard and its implementation. It is still not fully
implemented by several compilers. Many members of the committee have 
come to recognize that too many features were accepted into this 
standard. They are determined to ensure that a very high threshold be 
set for additions to future standards.

The straw vote among the members present was yes 3 - no 7 - abstain 1,
and the country vote was yes 0 - no 3 - abstain 3, see N1977. It was 
therefore decided not to apply for a new work item. The reasons for 
the no votes were predominantly associated with the delay in the 
implementation of Fortran 2003, the high cost of implementation of 
this feature, and the low level of requests for it from applications 
programmers. 

It was suggested that the promise to incorporate the specification into 
a future revision of the standard might be removed, but this did not 
meet with WG5 approval. Such a TS would not accord with the usual WG5 
practice nor with the requirements of the ISO/IEC JTC 1 directives, 
which say "When the subject in question is still under development or 
where for any other reason there is the future but not immediate 
possibility of an agreement to publish an International Standard, 
the technical committee or subcommittee may decide, by following the 
procedure set out in 2.3, that the publication of a Technical Specification 
would be appropriate."