Redstone Comparators

Redstone Comparators function similarly to redstone repeaters. However, it receives two signals.The redstone comparator has four functions: maintain signal strength, compare signal strength, subtract signal strength, and measure certain block states (primarily the fullness of containers).

If you want to make a quicker easier Redstone clock you can place a Redstone Comparator with a lever on its input end and wire from the lever past the side of the Redstone Comparator. If you have made it right the wire should start flashing (warning: if you put a Redstone repeater on the end of your wire it will stop working + don't forget to flick it once)