Solution to Challenge 1

Folding the test unit
1. Start with a square, fold in half and unfold. Fold both long edges to the centre crease and unfold.
2. Turn over, fold two opposite corners up and down to the nearest quarter crease.
3. Fold the long edges back in, tuck the triangular points over, then fold the unit in half.

Tabs and pockets
- The two tabs are the triangular points at the ends of the unit. They depend on the corner folds made in step 2.
- The two pockets are the openings along the inside of the folded strip. They depend on the long edges being folded accurately to the centre crease.

Checkpoint: the unit is a neat parallelogram with two points and two openings, and all creases are sharp.