One switch, two messages

A switch has two positions: down, or up. That is the whole switch.

A sender sets a switch. A reader looks at it. These are its two ends.

A bit can be pictured as one switch with two states. A state means something only if both ends agreed first.

A state is one position of the switch.

We write the two states as 0 and 1. The name is short for binary digit. A digit is one of 0 to 9. A binary digit is only 0 or 1. Nothing inside the switch looks like a digit.

One switch, read once, cannot tell three messages apart. The switch has only two states. "Now", "later" and "not at all" need more.

Can one switch say it?

Try the lab to finish this lesson.