Which side of the clock do I press?

Your own — the button or screen half nearest you. Pressing it stops your clock and starts your opponent's in one action. Place your stone first, then press.

Does passing use time?

Yes. A pass is a move: you pass and then press the clock, and the time you spent deciding to pass counts against you exactly like a normal move.

Should the clock stop during counting?

Yes. Counting is not thinking time and can take several minutes. By convention two passes in a row end the game and the clock stops for counting.

What if I forget to press the clock after moving?

Your own clock keeps running, and the lost time is yours. That is the accepted outcome — pressing is part of the move.

What if I press the clock by accident?

Say so immediately, because your opponent's clock is now running during your turn. On a clock with referee tools the time can be corrected without restarting the game.

Where should the clock be placed?

Flat beside the board, within easy reach of both players — at the side rather than between them, so nobody reaches across the board. Each player presses the half facing them.

How a Go clock works

A Go clock has two sides and only one runs at a time. You make your move on the board, then press your own side — that stops your clock and starts your opponent's. The clock measures thinking time, nothing else. Once main time is gone the display switches to your overtime — a byo-yomi period, or a block with a stone count — and the rules of that system take over.

The basic cycle

Black starts. Black moves first in an even game, so White's clock is stopped and Black's runs from the beginning of the game.
Place the stone, then press. Always in that order. The stone is played with your clock still running; pressing is what ends your turn.
Press your own side. The button or half nearest you is yours. Pressing stops your clock and starts your opponent's — one action, both effects.
Never press twice. If you press by accident you have started your opponent's clock while it is still your turn. Say so immediately; on a clock with referee tools the time can be corrected.

Which physical side belongs to whom is worth agreeing before the first move — on a phone, the half facing you.

What happens when main time runs out

The clock does not stop; it changes what it is measuring. What you see next depends on the system:

Byo-yomi: the display switches to a single period — say 30 seconds — plus how many periods remain. Move inside the period and it resets to full. Overrun and one period is gone permanently. Overrun the last one and you have lost on time.
Canadian overtime: the display shows a block of time and a count of stones you owe — 25 stones in 10 minutes. The clock runs continuously across those moves; completing the quota refills the block.
Fischer: nothing changes, because there is no overtime stage. The bonus was being added all along; if the clock reaches zero, the game is lost.
Sudden death: the game is over on time.

This transition is the moment most beginners misread, which is why a good clock makes it loud as well as visible.

Passing, and the end of the game

A pass is a move: you pass instead of placing a stone, and you still press the clock. Passing costs you time exactly as a normal move does.

By convention, two passes in a row end the game and the position goes to counting. The clock should stop there, because counting is not thinking time and can take several minutes. In Byoyomi Timer the pass buttons are on the clock face and a second consecutive pass asks for confirmation before stopping the clock for counting — so a mis-tap does not end the game.

Resignation ends the game immediately and needs no clock action, though a clock that records history will want to know the result.

Situations that come up in real games

Situation	What to do
You pressed without moving	Say so at once. Your opponent's clock is running in your turn; correct the time rather than playing on.
You moved but forgot to press	Your own clock keeps running — the loss is yours, and that is the accepted outcome.
Both players lost count of Canadian stones	Reconstruct from the board if possible, otherwise agree a count. This is why players usually take the required stones out of the lid and play from that pile.
The phone rang mid-game	The clock should pause. Agree the restart before resuming.
A period was lost to a mis-tap	Restore it with the referee tools; do not restart the game.
Disagreement about the time	In a tournament, the referee decides. Outside one, agree a correction and continue — the clock exists to serve the game.

Positioning a phone as a clock

Lay the phone flat beside the board, in easy reach of both players — traditionally at the side, not between the players, where hands cross over the board. Each player presses the half facing them, which is why both halves are rotated to face opposite directions: each player reads their own side upright.

Before starting, check the practical things: screen kept awake (the app does this), silent mode off if you want the spoken countdown, and enough battery for the length of game you intend to play. A three-hour title-match setting on a nearly empty phone is a bad plan.

Turn your iPhone into a real Go clock

Byoyomi Timer plays every Go time system — byo-yomi, Canadian overtime, Fischer bonus time, Ing — and reads the seconds aloud like a human timekeeper.

Coming soon to the App Store