Most experienced Access developers recommend that the Lookup Field Wizard be avoided. For reasons why see:
http://theaccessweb.com/lookupfields.htm
The same functionality can be achieved by binding a combo box to the column in question in a bound form, which is where data should be entered/edited, not in a table's datasheet view. For example, for an EmployeeID foreign key column a combo box could be set up as follows:
ControlSource: EmployeeID
RowSource: SELECT EmployeeID, FirstName & " " & LastName FROM Employees ORDER BY LastName, FirstName;
BoundColumn: 1
ColumnCount: 2
ColumnWidths: 0cm
If your units of measurement are imperial rather than metric Access will automatically convert the unit of the last one to inches. The important thing is that the dimension is zero to hide the first column.
Alternatively, you can concatenate the names so that the last name is first, which would be better with a large list of names as it allows the user to enter the initial characters of the last name and progressively go to the first match as each character is entered:
RowSource: SELECT EmployeeID, LastName & ", " & FirstName FROM Employees ORDER BY LastName, FirstName;