Stream API atb data interpretation??

[lewington]

So a typical change for a single selection/runner/horse might look like:

{"atb":[[1.01,1521.29],[1.03,27.96],[1.02,566],[3.55,108.41],[3.3,90.15],[3.05,101.14],[1.04,24.79]],"id":17022083}

I take this to mean that the following back opportunities are available in the market:

1.01 @ 1521.29
1.02 @ 566
1.03 @ 27.96
1.04 @ 24.79
3.05 @ 101.14
3.30 @ 90.15
3.55 @ 108.41

Is this the correct interpretation?

If so, I'm a bit puzzled: who exactly is laying this poor horse at $1.01 for ~$1500?

I have noticed that those very small priced lays turn up in a lot of updates, e.g. another change form the same batch of changes:

{"atb":[[1.01,1521.29],[2.32,15.91],[2.3,212.66],[1.03,20.8],[1.02,566],[2.2,172.79],[2.1,188.5]],"id":17873005}

Is this some kind of automated default lay amount that betfair makes on every runner or something?

One final thing, sometimes I see updates where all the volumes are set to 0, like the following:

{"atb":[[8,0],[6,0],[7,0]],"id":11815325}

The documentation seemed to imply that this means that the back prices $8, $6 and $6 used to be available in the market at some volume, but that someone has just cancelled all three (or possibly matched all three?). In this case Does that mean that there are currently no back opportunities in the market for that selection?

[LiamP]

Have you read the docs? It’s all in there.

Laying at 1.01 can be profitable assuming you are first.

[lewington]

Ah, thanks Liam. I found the part in the docs.

If I'm interpreting the wording properly, every tuple in "atb" represents the current state of the price point in question, and all price points are assumed not to change unless they are explicitly mentioned in a later update (except where the "img" flag is set to true?

so, assuming "img" = false

{"atb":[[10.00, 30.00]],"id":17873005}

means that the $10.00 price point for 17873005 has an open lay for $30 (in addition to whatever else was available before).

If the next update contains:

{"atb":[[11.00, 20.00]],"id":17873005}

This means there is a lay at $11.00 for $20.00, and the $10.00 price point is still at $30.00.

And if the next update contains:

{"atb":[[10.00, 20.00]],"id":17873005}

This means that nothing has changed at the $11.00 price point, but the $10.00 price point now has only $20.00 open.

Is that correct?

And if "img" = true, then the "atb" tuples represent the entire set of available price points (and everything else should be discarded).

Is that also correct?