The secondary weigh in, also known as the same day weigh in, requires a fighter to have added no more than 10lbs (around 4.4KG) over night. This idea is to stop fighters having unfair weight advantages come fight time though is a rule that only the IBF have.
Usually fighters manage to make the same day weigh in with no real problem and are inside the 10lb limit. Today, however,we saw Amnat Ruenroeng (12-0, 5) struggle with that second weigh in limit, coming in almost a full lb over his allowed maximum. Thankfully he managed to make weight half an hour later though it did leave some wondering if the champion was struggling at the Flyweight limit.
With the Thai only just able to make the secondary weight at a second attempt he'll be coming to the ring as a Super Bantamweight though Kazuto Ioka (14-0, 9) was around 120lbs himself and is unlikely to feel too disadvantaged by the weight difference.
As for the IBF Minimumweight title fight between Katsunari Takayama (26-6-0-1, 10) and Shin Ono (17-5-2, 2) both men made the same day weight on their first attempt.
(Image courtesy of boxingnews.jp shows Ioka and Ruenroeng at the original weigh in yesterday)