Some Information Is Discrete
Keyboard characters can be represented exactly
Imagine you and your friend are prohibited from talking -- its too noisy? -- and so you use dice to encode the letters and punctuation to communicate
With two dice there are 6x6 = 36 encodings, not enough for 26 letters, 10 numerals and punctuation. Three dice would give 6x6x6=216 representations, too many. So, you dump the numerals. Order matters: row then col!