The Basics:
- Binary on Wikipedia: https://en.wikipedia.org/wiki/Binary_number
- Hexadecimal on Wikipedia: https://en.wikipedia.org/wiki/Hexadecimal
- Decimal on Wikipedia: https://en.wikipedia.org/wiki/Decimal
- Numeral System on Wikipedia: https://en.wikipedia.org/wiki/Numeral_system
Binary Clocks:
- Binary Clock on Wikipedia, with an explanation of the different codings (binary-coded decimal vs. sexagesimal): https://en.wikipedia.org/wiki/Binary_clock