Power Query Table Group , help with Custom Comparer theory

Hi,

I recently came acrross a formula to group by a sum value ;

Table.Group custom comparer ;

I sort of get that in custom group (x,y)=> each time a true is returned a new group is started so ;

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But I recently found this formula and can't figure it out;

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so this will mean that the sum of units for each group < 50 , but I can't figure how the count for lList.Range , is working
so index x and y x = current y = next ?
so 2 - 1 + 1 = 2, 3 - 2 + 1 = 2 , 4 - 3 + 1 = 2, but if 2 is used the formula breaks so this cannot be what is happening ? All I can guess is that
the y value increases / iterates through until the condition is met, 2 - 1 +1 , 3 - 1 + 1, 4 -1 + 1 etc. ?

if anyone can help in explaining how this is working please do , I have read ( i think most of )
PQ how on this but it did not really help this, unless i missed that bit.

I have attached a work book with examples.

Richard.

Thank you both, that's sort of what I'd though must be the answer, not that I'm really sure, as said my initial thinking for the count was that it
would always = 2, but this was clearly not the case. regarding group kind, I did try a global group but it returned out of range,
which I think is looking for 12 in a list of 1 to 10.
Have not had a chance to look at the link but will do.

Thanks again.

RD