"一等三角測量とは" [About Class 1 Triangulation Stone Markers] (in Japanese). Geospatial Information Authority of Japan. Archived from the original on 27 April 2015. Retrieved 20 April 2015.
"一等三角点標石の構造" [Class 1 Triangulation Stone Marker Construction] (in Japanese). Geospatial Information Authority of Japan. Archived from the original on 27 April 2015. Retrieved 20 April 2015.
"一等三角測量とは" [About Class 1 Triangulation Stone Markers] (in Japanese). Geospatial Information Authority of Japan. Archived from the original on 27 April 2015. Retrieved 20 April 2015.
"一等三角点標石の構造" [Class 1 Triangulation Stone Marker Construction] (in Japanese). Geospatial Information Authority of Japan. Archived from the original on 27 April 2015. Retrieved 20 April 2015.