Not more than one hour before the voting begins, the election judges shall open the ballot box and show to all present that it is empty. The ballot box shall then be locked and the key kept by one of the election judges. The ballot box shall not be opened or removed from public view from the time it is shown to be empty until the polls close or until the ballot box is delivered for counting pursuant to section 115.451. If voting machines are used, the election judges shall call attention to the counter on the face of each voting machine and show to all present that it is set at zero.