1. 1. for example see: Wikipedia: “Nocturnal penile tumescence”. https://en.wikipedia.org/wiki/Nocturnal_penile_tumescence
2. 2. Kaneko S, Yachiku S, Miyata M, Mizunaga M, Watabe Y, Taniguchi N, Iuchi H, Matsuda H, Kurita T: Continuous monitoring of penile rigidity and tumescence in Japanese without erectile dysfunction. Nihon Hinyokika Gakkai Zassi. 82(6), 955–960, 1991.
3. 3. Kaneko S, Yachiku S, Miyata M, Mizunaga M, Watabe Y, Taniguchi N, Iuchi H, Matsuda H, Kurita T: Diagnosis of penile erectile dysfunction: simultaneous recording of nocturnal penile rigidity and circumference expansion. Acta Urol Jpn. 37(6), 1361–1366, 1991.
4. 4. for example see: Wikipedia: ”Postage stamp test”, https://en.wikipedia.org/wiki/Postage_stamp_test
5. 5. JIS-K-6253-3: Rubber, vulcanized or thermoplastic, determination of hardness, part-3: durometer method”, official copy distributed by Japanese Standards Association.