yeah!!! actually he uses a freaky trick for this,

the initial point is not obtainable from the model alone!!!!

but since I have no values I will explain how HE does it

the reference point is given at the beginning of the sequence it consists of:

using two edges which are perpendicular to each other in the initial square

imagine an L if you will

taking the centerpoint of one side of the paper and aligning it with the next edge of the perpendicular, while you at the same time align the the furthest edge of the perpendicular edge ( the corner) to the opposite paralell edge this gives a diagonal that crosses the first side and this is the reference for the gusset

Am I making myself clear? I don't think so so I will explain again

in a square we will number the sides in a clockwise fashion starting with a side called 1.

align the centerpoint of side 1 with the edge of side 2 and the corner between side 2 and 3 with the edge of side 4, a diagonal crosses from side 1 to side 3, the point of this diagonal touching side 1 is the reference for the gusset in locust Op. 430

after you fold the central birdbase and sink it use that reference on two places to locate the dimensions of the enpoints of the gusset

Hope this helps

X