A constant letter shift

Learning outcome

You can find a constant letter shift and use it to code a new word.

Concepts and reasons

A constant shift moves every letter by the same number of places. Write the place of each letter: A is 1 and Z is 26.

If CAT is coded as DBU, compare letter by letter. C to D is +1, A to B is +1, and T to U is +1. The shift is +1 for the whole word. Apply +1 to every letter of the new word. DOG becomes EPH.

The shift can be more than 1. MIND coded as OKPF is +2: M to O, I to K, N to P, D to F. A shift that fits only the first letter is not the code.

Worked examples

1. CAT is DBU. The shift is +1. DOG is EPH.
2. MIND is OKPF. The shift is +2. CAT under the same code is ECV, because C+2 is E, A+2 is C, and T+2 is V.
3. If each letter moves back by 1, DOG becomes CNF. D-1 is C, O-1 is N, G-1 is F.

Common traps

Do not reverse the word when the pairs show a shift. CAT reversed is TAC, but DBU is not TAC. Do not mix +1 and opposite letters. Opposite of C is X, because 3 + 24 = 27. DBU uses D, not X. This lesson does not wrap from Z to A. None of these words reaches Z.

Practice questions

1. If CAT is DBU, how is PEN coded?
2. If MIND is OKPF, how is DOG coded?
3. If each letter moves back by 1, how is SUN coded?

Answers and explanations

1. QFO. The shift is +1. P+1 is Q, E+1 is F, N+1 is O.
2. FQI. The shift is +2. D+2 is F, O+2 is Q, G+2 is I.
3. RTM. The shift is -1. S-1 is R, U-1 is T, N-1 is M.

Analogy

A constant shift is a parade in which every person takes the same number of steps. Count the steps on the first pair before you move the next word.

Quick reference

• Compare every letter, not only the first.
• CAT to DBU is +1. DOG becomes EPH.
• MIND to OKPF is +2.
• A reverse word is a different code.
• Opposite letters sum to 27. That is the next lesson, not this one.