Menu Messages\Rot 13 lets you code or decode a message in rot 13:

The screen is split up in two parts : the text to be decoded has to be typed in the top part, in the bottom part the text appears coded.

Rot 13 is not a real code but is sometimes used in a group to hide text. for example the answer for an enigma or quiz question. To decode a text it works the same.

The method used for coding/decoding : only the letter characters (capital- and letters, but without accents) are coded. For each letter a number is given: A=1, B=2, ... Z=26. To code you add 13 to the number and then the letter found in that position is used.

Example : A has the value of 1. Add 13 to code, so 1+13=14. the letter with number 14 is N, so A becomes a N.
To decode you do the same: N has a value of 14. 14+13=27, as a result you get 1 (27-26=1). The first letter is A, so the N becomes A.

If you rather code/decode yourself here is a coding table: