The coin below is the most extreme example of this type that I have managed to find, It has a doubled line at the bottom of the O in ONE, and this is the aspect that is most evident on all the examples that I have so far come across, but this particular coin also shows a partly doubled line at the top of the O. The design of O in this font type is slightly elongated from top to bottom, with fatter slightly less curved sides than are to be found at the top and bottom of the O. Its clear that the inner extra line at the bottom is straighter than the curvy bottom of the O itself , and this suggests to me that the inner line is the side of a 90 deg. rotated O showing below the over stamped correctly positioned O, its not a rare variety as I have found it on Rev. Freeman J pennies from 1875 to 1880, though It does seem a little scarcer on the 1878s than the other years, but you can only find it on Royal Mint coins, and not at all on Heaton Js. Its missing on the 1876, as this is a Heaton only year, and I haven't found any so far on the 1881s that I have looked at ??. As its found covering so many years, and indeed even can be found on proofs, it suggests that it was present on one of the master dies, with many working dies being made from it all carrying the same error. Your thoughts .