Diagnosis
Some columns can only take single values.
This can be due to one of the following reasons:

• Values in this column are used for validating and determining the
values in a different column that can only be interpreted incombination with the former. Consequently, the values in this columnhave to be determined uniquely.

• The way that the value for this column is encoded internally is
different to how this value appears externally. For example, acharacter value could be converted internally into a number. As aresult, the way the values are sorted internally is different.Likewise, an interval entered externally no longer corresponds ingeneral to the interval created using the internal values.