Complicated rules - but it's the atmosphere that really counts
The rules governing the Paralympics swimming classes can be bewildering, but they pale into insignificance once you get caught up in the action.
Six hundred swimmers are competing for a total of 148 medals at the Paralympics. At the Olympics, just 34 medals were up for grabs in the pool.
Paralympics swimming is divided into a mind-boggling number of classifications and events - so there are many opportunities to get a medal.
At the Aquatics Centre, my mind is not only occupied with Team GB's medal prospects, but also how to get a handle on who is swimming when, why, and if I'm honest, how.
A number of my fellow spectators have taken the bewildering complexity of it all in their stride and done their homework.
One - Peter - says he watched an explanation of all the classifications with his family before travelling to the Olympic Park from Manchester. He explains his understanding of the system.
"There's S1 to S10. They are all grouped with the same ability in each section."
This is just the tip of the iceberg. The classifications Peter refers to represent physically disabled swimmers and only cover freestyle, butterfly and backstroke events.
Most of these categories also have races in SM - individual medley and SB - breast stroke.
And that's not even all the categories.
S11 to S13 athletes have a visual impairment and S14s have an intellectual disability.
To make sense of it all, Peter and family have brought their tablet computers along to refer to as and when necessary.
Next I meet Anna, who has also been to the cycling - it's at least as complex in how it categorises riders. "I admit to I don't know the fine principles behind everything," she says. "When you see a British person you just cheer, that's the important thing."
And as the competition gets going, it is obvious most people have the same idea - a deafening cheer goes up around the Aquatic Centre.
Cheers turn to roars as British swimmers Nyree Kindred and Hannah Russell take silver.
And then it's time for the men's S7 100m, with Jonathan Fox representing Team GB. He broke a world record earlier in the day so hopes are high that he will get a gold medal.
As Fox and the other athletes take their positions, my sighted assistant points out their varying degrees of mobility impairment. Swimmers arrive to take part in the same race on crutches, in wheelchairs or supported by another person.
As Sarah, another spectator, reminds me on my way in to the stadium, "It is not about their ability to get to the water's edge, it is about their ability once they get in the pool."
The IPC's description of Fox's S7 category bears this out:
"This profile is designated for athletes with one leg and one arm amputation on opposite sides, double leg amputations or a paralysis of one arm and one leg on the same side. Moreover, swimmers with full control over arms and trunk and some leg function can compete in this class."
Fox - who has cerebral palsy - wins his race, nabbing Britain's only swimming gold of the evening.
Nineteen races take place over a four-hour period at this event. As we get to grips with the classifications, our attention is drawn to the impairments of the athletes.
As the stadium empties, I grab a chat with fellow spectator Lucy. She has been captivated by the various ways in which swimmers prepare for their events.
"I found it quite fascinating how they got in and out of the water. It makes it more real. And how simple it is to put their leg on. They just start walking again. It makes you realise how normal it is."
I arrived at the Aquatic Centre slightly bemused by all the different classes and events. But over the course of the session, as the action unfolds and medals are won, the complexity of the classifications matters less and less.
As foam-fingered volunteers wish us good night, I'm completely caught up with the Paralympic spirit.