Sangaku (算額), votive tablets with mathematical content, are a cultural heritage unique to Japan. The Sangaku Archive Project, a 3-year initiative based at the Waseda Institute for Advanced Study (WIAS) is an effort to document as many of ca 900 extant sangaku and of ca 1500 sangaku documented in literature in an open-access digital archive (see sangaku-archive.org). The project includes a considerable amount of data collection whereby sangaku need to be visited in their current location (usually a temple or a shrine), photographed and documented in situ. Whilst the majority of the data collection for the Sangaku Archive Project was conducted in AY2024 and the first half of AY2025, a considerable number of sangaku were documented in the second half of AY2025, partially financed by the Tokutei Kadai.Specifically, the funding received from Tokutei Kadai was used to buy a high-quality camera, and to contributed to the financing of two research trips of ca. 10 days each to document sangaku in various locations and participate in a conference. The first research trip was conducted in Kyushu in December 2025, visiting shrines in Oita, Kita-Kyushu, Fukuoka City and Saga to document the sangaku there, and participate in the 2025 Jinmonkom Symposium in Kyushu University.The second trip was conducted in Tohoku to investigate several sangaku in Naraha Town and Shinchi Town (Fukushima), as well as Yurihonjo (Akita) and a votive tablet containing a calendar held at Hachinohe City Museum (Aomori).During the funding period, I presented the Sangaku Archive Project at a symposium organized by IPSJ (Information Processing Society, Japan) in Ishigaki and published a paper in the WIAS Bulletin.  

Sangaku (算額) present a custom unique to Japan: as votive tablets showcasing mathematical problems, they were dedicated in temples and shrines throughout Japan, starting from the Edo period and well into the twentieth century. The central effort of this research project is devoted to the compilation of a bilingual digital archive of all sangaku (算額) surviving to date in Japan. Doing so, we hope to open up this rich cultural heritage to international scholarship and to put Japan’s idiosyncratic mathematical discourse on the map of the global history of mathematics.The project has commenced in April 2023 and will proceed for a duration of 3 years, in a continued effort to collaborate with researchers of the history of mathematics in Japan, temples, shrines, municipal institutions and other holders of sangaku. Whilst the metadata for each sangaku has already been obtained and converted into digital format, the bulk of the task now is to travel to shrines and temples to take high resolution photographs of the sangaku that still survive.Funding from the Tokutei Kadai Research Base Creation has been used to create the basic predicaments to make this project possible. Half of the funding was used to purchase a high-resolution digital camera and a high-quality lens suitable for taking photographs of sangaku. Since some of the sangaku are suspended in eaves or dark locations, the use of this special equipment has been indispensable for taking photos of a quality high enough to facilitate deep zooming. Since many sangaku are faded or otherwise degraded, this often means surfacing content that would otherwise not be visible to the naked eye.The other half of the grant was spent on travel expenses. Around 950 sangaku survive spread out throughout the country. The compilation of the archive therefore requires a considerable amount of travel to the respective locations. The funding from the Tokutei Kadai grant sponsored travel necessary for documenting ca 120 sangaku. Together with images obtained from other sources, this brings up the count to ca. 200 images, that is approximately 20% of the total amount of images to be made available in the final archive.