[originally this was described in CR-000076 but an inappropriate
solution was proposed].
The requirement is to be able to record values that happen to be
negative changes (e.g. a 5kg weight loss, which is recorded as -5kg) in
such a way that it is known that the change should be displayed
as a positive value, since the name of that value will imply the
negative, e.g.:
weight loss: 5kg