Countback methods vary by whether or not wasted and exhausted ballots are additionally used during the countback. The effect this has on the result of the countback depends on the differences in the next preferences of voters. Moreover, in STV systems that use exhausted ballots during countbacks, it becomes theoretically possible that the "order" of multiple resignations will affect who the ultimate replacements are - this is a consequence of the order of election as votes allocated to elected candidates are locked that value of which are no longer used in the determination of the election of further vacancies. Additionally, if ballots are allowed to be exhausted in the election, then by either method it remains possible that the chosen replacement will only meet a fraction of a quota of voters; when this fraction is particularly small, and therefore no similar candidates remain on the ballot, election rules may call for a different method of filling the vacancy to be used. The method is the calculation of a candidates surplus also contributes with a paper based formula (see above) complicating the countback process. A value based system being more accurate and less complicated. With the aid of computer based technology the results of a count-back can be determined immediately.