Parity bits are used to check that data has been transmitted accurately.
One or more extra bits are appended by the sender to the data as an accuracy
check during transmission.

There exist two types of parities: even and odd. The sender
inserts '1' or '0' parity bits so that the total number of '1' is even
or odd, including the parity bit. Assume, for example, that two hosts are
communicating with even parity. As the transmitting host sends data, it
counts the number of set bits. If the number of set bits is even, it sets
the parity bit to 0; if the number of set bits is odd, it sets the parity
bit to 1. Data bits can be arranged in an array for parity checking. In
this case a parity bit is inserted for each row and each column.

The application allows you to chose between even and odd parity. The array
is filled with random numbers and you should insert the right parity bits.
If you select the check box 'show errors' your answers are checked and
wrong answers marked.