 It is perhaps one of the most unfortunate phrases in NASA's vernacular, All Balls, and it caught the attention of a lot of people when I was doing my Apollo 13 live tweet. So what does it mean? That's what we're looking at today on Vintage Space. The phrase All Balls is another one that requires a little bit of a backstory before getting into what it actually means. The IMU, or inertial measurement unit on the Apollo command module, was a finely tuned instrument that gave the spacecraft its platform alignment so that when the crew had to do a burn, they knew the burn would be in the correct direction at the correct angle or attitude. But as I mentioned in a previous video about gimbal lock right here, the platform could drift, which meant that the crew had to constantly realign it during a mission to the moon. This platform alignment was done in two ways. The first had the command module pilot do star sightings. He would pick two stars, knowing where they were in space, and try to line the spacecraft up with those stars using the sextant. That would make sure that he was angled in the right direction. At the same time, the spacecraft would do its own star sighting. With the spacecraft at a steady attitude, the sextant was turned towards one star. Once a star was lined up, a button signaled to the computer at the mark of the star's position and lined it up to that point. Then the sextant did the same thing on a second star. Once those two stars had been sighted, the computer would display the degree of error to the crew in the spacecraft as well as to the men in mission control. From there, the engineers could figure out just how much to gimbal the engines to get the platform back in alignment. And like everything the astronauts did, there was a competitive aspect to this platform re-alignment. And here's where All Balls comes in. Because the command module pilot and the computer were doing the star sightings at the same time, it became a mark of pride for the command module pilots to do a perfect alignment. Part of the P-52 program was to give the astronaut a degree of difference between his measurements and the computers. If there was no difference, if he had done a perfect star alignment, he gave him five zeros, or All Balls. And with all the chatter between a spacecraft in Houston on the way to the moon, it was far simpler for the astronauts to just say All Balls as opposed to explaining that they had done a perfect P-52 alignment. Although most drove at home by referencing, again, that they had done a perfect P-52 alignment. And perhaps unfortunately, the phrase All Balls is still in NASA's vernacular, even on unmanned missions. It is still a shorthand for saying no error. So what do you guys think? Is All Balls potentially the most awkward thing astronauts said to Houston on their trip to the moon? Let me know in the comments below, and of course, if you have ideas or topics you'd like to see covered in future episodes, leave those in the comments below as well. For Vintage Space content every single day of the week, be sure to follow me on Twitter as AST Vintage Space. And I've got new episodes going up every single Tuesday and Friday, so subscribe right here, so you never miss an episode.