At all elections at which voting machines are used the exterior of the voting machine and every part of the polling place shall be in plain view of the managers and clerks, if there be clerks of election. The voting machine shall be placed at least three feet from every wall or partition of the polling place and at least five feet from any table at which any of the election managers or clerks, if there be clerks, may be engaged or seated. The voting machine shall be so placed that the ballots on the face of the machine can be plainly seen by the managers of the election when not in use by voters. The managers of election shall not themselves be, or permit any other person to be, in any position or near any position that will permit them to see or ascertain how a voter votes or how he has voted.