How can you determine, without measuring any angles, weather a quadrilateral is a rectangle?

Answer 1

If we are allowed linear measurements, we can check:
1. If both pairs of opposites sides are equal. If this is the case, it is a parallelogram, then and only then,
2. If both diagonals are equal, the figure is a rectangle, then and only then,
3. Finally, if adjacent sides are equal, the figure is a square.
No angle measurement is required.