Jurisdictions purchasing equipment and states appropriating funds for equipment should ensure that the new equipment gives the jurisdiction maximum flexibility to adopt any legal voting system. Most modern voting equipment is compatible with all voting systems and ballot types, but the only way to ensure compatibility is to include a provision in the Request for Proposals or appropriations bill. This will not add to the cost of the equipment in most cases, but it could save the cost of an expensive upgrade in the future.
A single line can be sufficient:
"Funds may only be appropriated for purchasing or upgrading voting equipment and software that is compatible with all ballot types currently used in public elections in the United States."
It may make sense to specify that this includes ranked-ballot systems and that in such systems, voters rank candidates in order of choice and the voting equipment stores a record of each voter's ranking:
"A ranked-choice ballot is one in which voters may rank candidates on the ballot in order of preference, and the record of each ballot's set of preferences is preserved."
For reference, here are the 4 ballot types currently used and the voting systems that use each one in parenthesis. These systems allow voters:
- To vote for one candidate (plurality, runoff, limited voting)
- To vote for more than one candidate (at-large plurality, limited voting)
- To give more than one vote to one or more candidates (cumulative voting).
- To rank candidates in order of preference (instant runoff voting, choice voting)
With ballots types 1, 2 and 3, the number of votes for each candidates is simply added up, and the candidate or candidates with the most votes win.
With a ranked-choice ballot, voters must be able to rank candidates on the ballot in order of preference, and the record of each ballot's set of preferences must be preserved. The voting equipment creates an anonymous datafile containing a record of each voter's rankings. To determine the winner(s) of the election, the datafile is fed into ballot counting software or the ballots are sorted and counted by hand.