Mo. Rev. Stat. § 115.249: Standards required of voting machines.

No voting machine shall be used unless it:

(1) Permits voting in absolute secrecy;

(2) Permits each voter to vote for as many candidates for each office as he is lawfully entitled to vote for, and no other;

(3) Permits each voter to vote for or against as many questions as he is lawfully entitled to vote on, and no more;

(4) Provides facilities for each voter to cast as many write-in votes for each office as he is lawfully entitled to cast;

(5) Permits each voter in a primary election to vote for the candidates of only one party announced by the voter in advance;

(6) Correctly registers or records and accurately counts all votes cast for each candidate and for and against each question;

(7) Is provided with a lock or locks which prevent any movement of the voting or registering mechanism and any tampering with the mechanism;

(8) Is provided with a protective counter or other device whereby any operation of the machine before or after an election will be detected;

(9) Is provided with a counter which shows at all times during the election how many people have voted on the machine;

(10) Is provided with a proper light which enables each voter, while voting, to clearly see the ballot labels.