After strugling to connect to a device for the past few hours only to find that it had a "ODD" parity bit in its connection settings, I have to ask.
Why have an Odd, Even, None, parity bit?
I can understand the reason to have one of the three types (error checking) but why all three. It seems like its created just to annoy system integrators.
It's just a quirk of the old serial port specifications.
In order to get two serial devices to communicate, the baud rate, parity, and stop bit settings had to all be correct. It gets worse, because there were some intricacies in the way the connections were wired together, the use of software vs hardware handshaking, DTE vs. DCE, etc.
There are different types of parity because different groups had their own way of doing things. It's the same reason there are multiple standards for many things.
Why do people in some countries drive on the left, in others on the right?
In the bad old days various pieces of hardware had these choices hardwired. So software tools had to be adaptable.
And why did different pieces of hardware do it every which way? Pure expediency. Standards don't develop without (a) a central authority from the beginning or (b) plenty of time to shake down the choices and develop consensus. Well, electronics has never had a central authority (and good riddance, distributed decision making explores more of the available design space better and smarter), and the experience needed for shaking down is gained by trying all the ways, included the wrong ones and the multiple equivalently right ones. So each engineer makes the choice that get this project done /^[fast|cheap|good]{2}$/.
Welcome to the marketplace of ideas.