When the E-115 was adopted by Mattel as an addition to the Barbie™ product line, it was aimed mainly at girls with a minimum age of 5 years. For this reason the product was given a pink-and-purple case and the Barbie logo and image were printed on the body.
As it was probably thought that secret writing would not appeal to girls, the coding/decoding facilities (using one of 4 built-in cipher modes) were omitted from the manual. Nevertheless, these facilities can still be accessed if you know how to activate them.
http://www.cryptomuseum.com/crypto/mehano/barbie/#coding
Islands of Math 