One specification (in at least in one large county) which complicates the design of the voting machines is the one that requires that the votes must not be recorded sequentially. I presume that they do not want anyone to be able to determine which voter cast each ballot. The Registrar will not allow a scheme in which the data can be recorded like in a ledger book.
Here's a recent story of the testing of the voting system in Riverside County, California.
DOWN FOR THE COUNT