Sand Box John wrote:"dcmike"
FYI a parity bit is no longer used on any of the destination sign systems. That trainline was reassgined to the 80s bit to allow for destination codes up to 99. Theoretically higher values could be stored but the input hardware and display on the operator's console is limited to two digits.
So for my recreated sign roll artwork I should remove the parity stripe to be compatible with the existing rolling stock?
Mind you all of the codes that would use the 80s bit in today's schema are non revenue destination codes that display No Passengers.
It's your sign, do as you please
I think you can improvise, making the assumption that rollsigns made it to the silver line opening. You can reassign the parity bit to read CV 80 (which you would remove on your Ashburn sign) and do the math from there.
I will say that given that Metro replaced the rollsigns with digital signs in the late 1980s, the parity bit would be obsolete by then since you don't need to confirm the position of a digital sign.
However, one can sacrifice the parity for the sake of additional readings. You only have to make sure that your curtains are in good shape