Fitz tells Simmons that he broke his arm in the same place as he did in '2nd grade' , but Fitz is Scottish and in Scotland the schooling system doesn't go up in grades but instead calls each year 'primary one , primary two , etc' ,the Scottish equivalent to '2nd grade' is primary four so he would have never been in 'second grade' and neither would Simmons as she is from England and would have been in 'year three' instead of 'second grade'
Fitz tells Simmons to fill her lungs from an oxygen tank and hold her breath as she swims to the surface from a depth of 90 feet. Anyone who does this will burst their lungs and die.
When Fitz and Simmons are trapped in the pod at the bottom of the ocean, they are talking about "doing the math" of their situation. In the UK, mathematics is referred to as maths, not math.