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Standard uncertainties (SU) in the DDLm dictionary

  • Subject: Standard uncertainties (SU) in the DDLm dictionary
  • From: Antanas Vaitkus <antanas.vaitkus90@xxxxxxxxx>
  • Date: Wed, 12 Apr 2017 12:44:43 +0300
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I have several question about the way standard uncertainties should be specified to conform to the new DDLm dictionary. The definition of the "Measurand" enumerator value in the _type.purpose save block states that:
  This value must be accompanied by its standard uncertainty
   (SU) value, expressed either as:
    1) appended integers, in parentheses (), at the
         precision of the trailing digits,       or
    2) a separately defined item with the same name as the
         measurand item but with an additional suffix '_su'.

Several question arise from this definition:
1) Can the ways of expressing SU be used interchangeably?

For example, if the have a separately defined data item with the '_su' suffix in the dictionary, is it still allowed to specify the standard uncertainty using the parentheses ()? Consider the following situation:

If we have the following definitions in the dictionary that the CIF file conforms to:

Can we write the following in a valid CIF file:
    _measured_value   3.14(42)

Or is is strictly:
    _measured_value        3.14
    _measured_value_su 0.42

2) Does one way of expressing SU values have precedence over the other?

For example, If we have a CIF file with SU specified using both, the parenthesis () and the separate data item with differing values, should one of them be considered the preferred one?
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