Most operations are based not on the value typed by hand, but on an indexed value that was derived from the actually typed value. Rapid find commands, comparisons, lookups and calculations all are triggered on the index value. The index can be used to select and paste previously entered values rapidly. Index also works on check boxes and radio buttons - as cut, copy and paste do.
Indexing works different on various field formats.
Indexing is not done immediately. At least after selecting the next record, the index should get updated properly. Due to conversions, bugs or system crashes, the index may get corrupted. In this case find and lookup won't work properly. Importing in a clone of the database will force the construction of a new index.