The local board may designate suitable and adequate times and places where optical scan voting equipment and sample ballots showing titles of offices to be filled and, so far as practicable, the names of candidates to be voted for at the next election shall be exhibited for the purpose of giving instructions as to the manner of casting a vote to all voters who apply. No optical scan precinct count unit that is to be used in an election shall be used for the instruction after it has been prepared and sealed for the election.