Japanese Datum of Leveling

 This page explains the "Japanese vertical datum". and I quoted inferior web sites and wikipedia.


 When we measure Levels of grounds, we need the datum line of levels.
 Strictly, it is the average level of the ocean's surface. However, practically speaking, it is better we have the datum on the ground. Then, the Japanese government placed the inferior structure called "warehouse of vertical datum" in 1981 to keep the point of vertical datum.

"Warehouse of Vertical Datum"

 This building, like a roman shrine is located on the level of 24.3900 meters. And the place is based on a so strong stratum of to meters not to subside.

↓ Here is an explanation written in Japanese by the Geographical Survey Institute.
http://www.gsi.go.jp/kanto/ki8bsuigenten.html



There are some chances to see the inside of the structure. Please read the inferior Japanese web site.
http://www.mizunotec.co.jp/doboku/suijun_genten/suijun_genten.html