a method for detecting errors in data communications or within a computer system by counting the number of ones or zeros per byte or per word, including a special check bit (parity bit) to see if the value is even or odd.
The parity check symbols are appended to the trailing end of the sequence of data symbols.
Presumably, the parity check on the vertical sense bits would result in the message being discarded.
British Dictionary definitions for parity check
a check made of computer data to ensure that the total number of bits of value 1 (or 0) in each unit of information remains odd or even after transfer between a peripheral device and the memory or vice versa