The name the other player sees, and how strong you are. Neither changes how the game is played: the rank is never used to work out a handicap, it is just what the other player sees next to your name.

The rank is required: the game will not start until both of you have picked one. It goes down to 30k, which is where you start if you have never played.

Which side you take. There are two seats, so picking one hands the other to your opponent.

The side of the goban. 19 is the full board; 9 and 13 play much faster. It also changes the feel of the pace: on a small board a move covers more ground, so the zones take longer to close.

How often, on average, you get to put down a stone. Everything else follows from it: how fast your own zone shrinks back, and how long the board waits in silence before the game closes itself. Below the shortest pace there is one last notch, infinite (spam go): no zones at all, no ko — you play wherever you want, as fast as you can click, and only the rules of go are left. The handicap survives, measured on a made-up pace of a third of a second a stone, because at that speed white needs it more than ever.

A head start for black. White starts with the whole board off limits except a hole in the middle that widens over time — and in go the opening is in the corners, so being stuck in the middle costs real ground.

1 stone opens the hole straight away; every extra stone is one more move of closed board first. Half stones work too. To handicap black instead, take white yourself.

At infinite pace there is no move to count, so a stone is worth a third of a second — an arbitrary figure, roughly how fast a quick hand clicks. It makes for a short handicap, but at that speed a fraction of a second is a whole opening.