The zero mark of the mine
The zero mark of the mine is located west of Alfred Merry's shaft (the inclined shaft). All maps of the mine use this zero mark as point of origin for horizontal and vertical measurements. Therefor, when it was said that the new vertical shaft went 402 m down, this was 402 m below the zero mark. The shaft opening was 20 m above the zero mark, which made the actual depth of the shaft 422 m.