A drawer is judged by one thing: how it feels when you pull it. And that feel is decided by air.
A drawer that fits its opening exactly will bind, because the air trapped behind it has to escape past the sides as the drawer closes and be replaced as it opens. Too tight and it thumps and resists; too loose and it rattles and drops at the front when it is pulled out.
So our artisans fit each drawer to its own opening rather than to a specification - every drawer in this unit is made for one particular hole and marked so it is never swapped - and they leave a deliberate clearance at the back and at the top for the air to move, while keeping the sides close where the drawer runs.
Then it is tested by hand, loaded and empty, and eased where it needs easing. A drawer that runs beautifully when empty and stiffens when full has not been finished, only fitted.
It is slow, and it is the only way to get a drawer that still runs sweetly in twenty years.