Minecraft wiki entry for Clock, associated text: 1 Introduction
2 Torch clock
2.1 Rapid pulsar
2.2 Torch loop
3 Repeater clock
4 Torch-repeater clock
5 Comparator clock
5.1 Subtraction clock
5.2 Fader pulser
5.3 Alternating clock
6 Hopper clocks
6.1 Hopper clock schematics
7 Dropper-Dropper clock
8 Despawn clock
9 Command block clock
10 Piston clock
10.1 Minimal Piston Clock (A)
10.2 Minimal Dual-Piston Clock (B)
10.3 Dual Block Piston Clock (C)
10.4 Compact Sticky Piston Clock (D)
10.5 Advanced 1-tick Piston Clock (F)
10.6 Simple 3-gametick Piston Clock (G)
10.7 Self-Powered Piston Clock (H)
11 0 Tick Piston Clocks
11.1 1-output 3-gt clock
11.2 2-output 3-gt clock
11.3 1-gt clock
12 Minecart clock
13 Observer clocks
14 Long-period clocks
14.1 Clock multiplier
14.2 Redstone Repeaters with Feedback
15 References