A hidden sort key is added to the output for sorting in sortable tables. The sort key is based on the main value (parameter |1=) and, if used, the exponent for the power of 10 (parameter |e=) and/or units (parameters |u=, |ul=, |up= and/or |upl=). Where necessary, units are converted to base SI units for the purpose of the sort key, which is produced by {{ntsh}}. Several units are covered; see § How to add units for those which are not. To omit the sort key use |sortable=off.