It previews your responses on the screen to check and see if it was what you checked...You correct errors and if it still doesn’t record correctly...
you then need to call someone over to correct mistakes if possible and pull the machine if not..
But this only confirms the input is marked correctly.
The software reading the ballot, and then incrementing values, can do anything the programmer devised it to do.
The software can perform incorrect math, or it can simply add 10 votes to column A and subtract 20 votes from column B. Or it might ignore all the votes and simply report a predetermined total.
Furthermore, one of the polling staff might, independently of any voter, simply walk over to a machine and vote 50 times for candidate X, or feed in 90 ballots for candidate Y.
Solution:
Voters should get a unique ID number and a physical item carrying that ID number. Every vote/ballot should receive yet another unique vote number. Every voting record should come coupled with the voter's unique ID number, the unique transaction number of the vote, and a record of each item on the ballot. And date, time, location....
Leaving the polling station, the voter should receive two versions of his vote, one in clear text and one encoded. Each would hold all three pieces of info: voter number, vote number, and ballot choices. The voter might choose to destroy the clear text receipt there at the polling station.
With this, an individual voter would be able to, ten years after the vote, go online, enter his voter number and ballot/vote number, and compare his paper receipt with what the system claims was his vote.
None of this would stop fraudulent algorithms or poll-worker multi-voting or manipulation.
A partial solution would be to print physical copies of two receipts per vote. One goes home with the voter. One stays with the county election board. The board copies would be and should be used for recounts. These should be done as a matter of course. AND these should be checked for non-unique voter ID numbers.
We could do all this.