Modify this to be consistent:
This may cause ballots to be counted as invalid if the wrong system is used. If a voter puts a first-past-the-post cross in a numbered single transferable vote ballot paper, it is invalidated.
This may cause ballots to be counted as invalid if the wrong system is used. For instance, if a voter puts a first-past-the-post cross in a numbered single transferable vote ballot paper, it is invalidated.