Solution to Challenge 3

Where each part comes from
- Body: the middle of the bird base, which is the preliminary base after its petal folds on the front and back.
- Wings: the two upper flaps of the bird base, folded down at the end.
- Neck: one of the two narrow bottom flaps of the bird base, narrowed with kite-style folds and then folded up with an inside reverse fold.
- Tail: the other narrow bottom flap, treated the same way and folded up the other side.
- Head: the tip of the neck flap, with one more small inside reverse fold.

So the crane is the preliminary base, then the bird base, then reverse folds to make the two ends and the head.

Changing the sheet-count script

w, h, q = 210, 297, 100
per = (w // q) * (h // q)
print('A4 sheet:', w, 'x', h, 'mm; squares of', q, 'mm per sheet:', per)
print('Sheets for 1000 squares:', -(-1000 // per))

Output when run:

A4 sheet: 210 x 297 mm; squares of 100 mm per sheet: 4
Sheets for 1000 squares: 250

Comparing with the 75 mm case
75 mm squares gave 6 per sheet and 167 sheets, while 100 mm squares give 4 per sheet and 250 sheets. The squares are a third wider but need half as many sheets again (250 against 167), because the squares are 1.33 times wider and 1.78 times larger in area, and some paper is wasted at the edges when the sheet is not an exact multiple of the square size (here 10 mm across and 97 mm along).

Checkpoint: your crane should have a clear neck, tail and head, with the wings able to move. A crane with wings that will not separate usually means the petal folds were not fully flattened.