There was also a subtle difference in the feed hole location. On most formats. the center of the feed hole lined up with the center of the data holes. On a few older computers, the leading edge of the feed hole alisned with the leading edge of the data holes. The reason was related to whether the sensors were mechanical or electronic. I have data tapes of both types. To use only one reader, I added a switch enabled delay to the feed hole signal. Otherwise the leading edge type can give marginal data signals on a reader set up for center line format. Billy Pettit