An error-detection system for 5-unit-code teletypewriter transmission

For many years teletypewriter users have operated without automatic means for detecting errors. This was principally because a large part of the transmitted material was ordinary English text with a redundancy so large that for the most part there was no difficulty in reconstructing a misspelled word. For example, recognizing that ??enginaer?? means ??engineer?? was simple and obvious. For the correct transmission of numerals various expedients were used, such as sending all numerals twice, spelling out the words, as ??one,?? ??two,?? and ??five.??