Is an arrangement I made myself saved?

No. What you place lasts for that run only. The only things kept are records such as how far the chain reached.

Why does it stop partway?

Either the gap is too wide or the turn is too sharp. When placing by hand, moving your finger more slowly puts the tiles closer together. The five ready-made arrangements are built with gaps that carry through to the end.

What does the Daily Dopa compare?

How far the chain reached on that day's arrangement, as a percentage. The grade bands for this one are not taken from a measured distribution like the others — automated play reaches 100% almost every time, so there was no spread to cut — and are set in advance instead.

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Breaking

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Let it lay them out, or do it yourself. Either way, you push the first tile.

How to play

Press Auto and you get one of five patterns. Then tap the first tile. Switch to By hand and tiles stand up along the line you draw.

Notes on the feel

The gap before the last tile falls is stretched out a little. If nothing happens at the end of a chain, all you are left with is how quickly it was over. When a run stalls, the place it stopped lights up, so the next attempt only needs one fix.

What is this, really?

Domino toppling is a pastime with an absurd ratio between the time spent setting up and the time spent watching. The Guinness World Records entry for "Most dominoes toppled by an individual" stands at 321,197, set by Liu Yang of China at the Citic Guoan Grand Epoch City in Beijing on 31 December 2011; the record page notes that he set up the 321,200 dominoes between 23 November and 31 December 2011. More than five weeks of placing, and a few minutes of falling.

The reason people keep doing something that does not add up is, I suspect, that those few dozen seconds pay back all of the placing at once. Your job ends at pushing the first tile; from there physics does the rest. There are not many pleasures that continue after you have taken your hands off.

How it is done where it comes from

Setting up for real, a gap of about half to two thirds of a tile's height topples reliably. Too close and a tile lies down before it reaches the next one; too far and it never arrives. On a long run the standard trick is to leave deliberate gaps — safeties — so that one mistake does not take the whole line with it, and to fill them in last.

Here you can skip the placing altogether. Press Auto and you get one of five arrangements: a spiral, a wave, a branch and so on. Switch to By hand and tiles stand up along the line you draw with a finger. The pitch climbs as they go down, and the gap before the final tile falls is stretched a little on purpose — if nothing happens at the end of a chain, all that is left is how quickly it was over. Where a run stalls, the place it stopped lights up, so the next attempt only has one thing to fix rather than a whole line to re-examine.

Questions people ask

Is an arrangement I made myself saved?: No. What you place lasts for that run only. The only things kept are records such as how far the chain reached.
Why does it stop partway?: Either the gap is too wide or the turn is too sharp. When placing by hand, moving your finger more slowly puts the tiles closer together. The five ready-made arrangements are built with gaps that carry through to the end.
What does the Daily Dopa compare?: How far the chain reached on that day's arrangement, as a percentage. The grade bands for this one are not taken from a measured distribution like the others — automated play reaches 100% almost every time, so there was no spread to cut — and are set in advance instead.

Sources

Dates, names and definitions above are written only as far as the material below confirms them.

Guinness World Records, "Most dominoes toppled by an individual"321,197 / Liu Yang (China) / Citic Guoan Grand Epoch City, Beijing, China / 31 December 2011 / "Liu Yang set up the 321,200 dominoes from 23 November to 31 December 2011"

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