Biro with reversed 18-55mm kit lens set to F11 at 18mm and close focus
The reversed lens gives us a 5:1 macro (X5), the same as the
Canon MP-E 65mm macro lens at a fraction of the cost.

You set the lens for F11 whilst on the camera in Av and then pressing "stop down preview".
You then remove the lens whilst holding the stop down preview with the camera still on.
The rule is graduated in mm intervals