Puzzles/Geometric Puzzles/Rubber Band/Solution 1
Stretch the rubber band, and draw a line along it on the plane.
By stretching the rubber band, while holding the loose end to the nail, you can measure 4cm. By folding it again, you can measure 2cm. Similarly, you can measure 1cm and then 0.5cm. Mark the 0.5cm on the line, and using the last 0,5cm of the rubber band, mark the line you drew at 0.5cm intervals, so you can use it as a ruler.
Draw two circles around the nail, with radius 1.5cm and 2cm. Using 6cm of the rubber band, make a triangle, with a corner touching each circle, and the last corner at the nail. You now have a right angle at the nail.