A good answer might be:

• The ignition switch of an automobile.  No
• The hour hand of a clock.  No
• A button on a hand calculator.  Yes
• The volume control on a stereo.  No

The ignition switch of an automobile is discrete---it has definite states---but there are usually more than two states (off, running, start, acc...) A button on a hand calculator is a binary device. It is either on or off. Ordinarily it is "off." When you push it, it is "on." It springs back to "off" when you release it, which is different from a toggle switch, but it still is a binary device.

There are many advantages to binary. Here are four (somewhat overlapping) important reasons for using binary:

1. Simple; easy to build.
2. Unambiguous signals (hence noise immunity).
3. Flawless copies can be made.
4. Anything that can be represented with some sort of pattern can be represented with patterns of bits.

Simple; easy to build: An on/off switch is simpler and easier to build than a light dimmer. An accurate dimmer (where 25% means exactly 25%) is extremely hard to build. The same is true for the tiny devices inside a silicon chip. Easy to build means that the devices are cheap, small, and reliable, and that you can put millions of them in a small area.

QUESTION 3:

• Chisel out each book on stone slabs.
• Write each book by hand on paper with a pen.
• Carve a flat wooden block with the text of each page and use it with an ink pad to transfer the text to paper.
• Set each page with movable type and print as many books as you want with ink on paper.