Solution to Challenge 2

Folding the box and lid
1. Fold the 15 cm square: halves both ways, corners to the centre, then edges to the centre line, unfolding to leave the grid of creases.
2. Raise the walls and lock the corners with the flaps.
3. Fold the lid from the 16 cm square in exactly the same way.

Testing the fit
Place the lid on the box and slide it down. It should go on with a little resistance and come off without force.

If it is wrong
- Lid too loose: the lid paper is too big, or the box walls were folded slightly short. Check the box floor is close to 5 cm.
- Lid too tight: the lid creases were not folded to the centre line, or the box walls bow outwards. Re-crease and square the corners.
- Walls uneven: the thirds are unequal. Unfold, then check the creases with a ruler.

Checkpoint: the box has four straight walls, the corner flaps lie flat, and the lid fits with only a small amount of play.