Have got absorbed by the National Cipher Challenge.  Not sure what this animation varying the multiplier in an ‘Affine Shift’ add 5.  Functional grid shows transition from Caesar Shift 5, multiply by 1, through to multiply by 13, which is a useless cipher.  In fact any multiplier not co-prime with 26 can be seen to be not one-one, and therefore useless too.  Modular arithmetic, straight line graphs, ciphers, dotty patterns, ….