LOOKDOWN command question

[Russ Kincaid]

Chuck Hellebuyck's book states that the command is: LOOKDOWN search, (constant {, constant}), var. 'search' is a word or bit that is searched for a match to 'constant'. If a match is found, the position of the matched constant is stored in 'var'. Zero = first constant, 1 = second constant, etc. What happens if no match is found?

[rhino]

The PBP manual states:

Thus, if the value is found first in the list, Var
is set to zero. If second in the list, Var is set to one. And so on. If not
found, Var remains unchanged.