I don't how familiar you are with arrays, but knowing that arrays are zero-based is key to understanding all that. Zero-based means the first item has an index of 0. So the second item would have an index of 1, the third item would have an index of 2, and so on.   And think about it in terms of math. How many screen widths is the first panel away from the viewport? It's already in view, so that would be 0. The second panel is 1 screen width away, the third panel is 2 screen widths away
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