I am indexing a book entering items in order of appearance, and setting up subtractions to give a column with the lengths of each item. When I sort them into alphabetical order, the item lengths are altered.
Hello.
Please see this topic about updating cell references while sorting data. Pay attention to @Lupp provided information - there are issues when Update references... are enabled.
You can also copy information needed to new sheet using Paste Special and copying only values, not formulas, so after sorting this new sheet values will be kept unchanged.