O in Morse Code

How long O takes

O is 0 dots and 3 dashes. With the gaps that comes to 11 units, number 20 of 26 by length.

• 5 WPM: 2,640 ms
• 13 WPM: 1,015 ms
• 20 WPM: 660 ms

The arithmetic behind them is on the timing page.

What O gets confused with

4 characters sit one element away from O:

• G --. - a dot in third place instead of a dash
• K -.- - a dot in second place instead of a dash
• M -- - the last dash missing
• W .-- - a dot in first place instead of a dash

O in the tree

• Built from: - = T and -- = M, then ---
• Carries on into: no other letter - a leaf of the tree
• Backwards: --- = itself, a palindrome
• Koch position: 10 of 26

The tree shows the whole shape, the trainer teaches it by ear.

Why O has this code

O makes up about 7.5 per cent of English text, which is number 4 of 26 by frequency, against number 20 by length. That is a mismatch in the expensive direction: O turns up more often than its code length allows for, so it costs airtime on every message.

The lengths were set by counting, not by theory - the alphabet page has that story.

O in American Morse

The American code, used on the landline telegraph until the 1920s, wrote O as . . instead of ---. Note the gap inside the character: American Morse used internal spaces, which is what made it so hard to read automatically and why the international code replaced it on the radio.

The full table has the other ten.

Worth knowing about O

O is the middle of SOS - the three dashes between the two runs of dots. It is also the clearest case of a common letter with an expensive code: fourth most common in English, and eleven units long.