Does it matter?
It's the magnetic moment of a proton and antiproton that has been measured as being equal, hence more confirmation that antimatter is the exact equal but opposite of matter. This makes it even more puzzling as to why there is so much more matter than antimatter in the observable universe.
The theory is that equal amounts of matter and antimatter should have been created in the Big Bang, which should then have gone on to destroy each other. One idea was that small differences between the deep structure and properties of antimatter and matter made it more likely that matter would somehow be preferred over antimatter. This idea is now looking less likely.