In any county, city or town in which voting machines are to be used, the board of voter registration and elections or other electoral board may designate suitable and adequate times and places for the exhibition and demonstration of a voting machine containing sample ballots, showing the title of offices to be filled and, so far as practicable, the names of the candidates to be voted for at the next election for the purpose of giving instruction as to the use of a voting machine to all voters who may apply for it. No voting machine shall be used for such instruction after being prepared and sealed for use in an election. During such exhibition the counting mechanism of the voting machine shall be concealed from view.