IN-4 nixie tubes: http://www.tube-tester.com/sites/nixie/data/in-4/in-4-sh2.htm

SN74141 drivers: https://tubehobby.com/datasheets/k155id1.pdf

74HC595: https://www.ti.com/lit/ds/symlink/sn74hc595.pdf

DS3231: https://www.analog.com/media/en/technical-documentation/data-sheets/DS3231.pdf