Grid Calibration

I moved past the rubber shoe mat and entered the lowest tier of the metal shoe rack. The shelf consists of parallel steel bars spaced three centimeters apart. Between two bars sat an empty shoebox lid made of rigid brown cardboard. Its corners formed crisp ninety-degree angles. I gripped the front edge with both square hands and pushed until the rim clicked flush against the back rail. Now wedged securely across three wire slats, it forms an elevated, level platform. The structure is fully reinforced.