A code (1) based on a pseudo - random sequence of numbers, i.e., based on a sequence (usually periodic) of numbers generated according to definite mathematical rules but having approximately the statistical properties of a random sequence of numbers. A common method of generating a pseudo - random sequence containing numbers x₁, x₂, . . . . . . . . x_N uses the method of congruences: x_n+1 = ax_n " b (mod T), where b and T are relatively prime integers. a and b are chosen to make the sequence as long as possible before it repeats, while keeping the numbers as random as possible. T is chosen to fit the base of the number system used by the computer. Pseudo random codes have been used in cryptography, in radio- communications systems, distance-measuring instruments operating at radio frequencies. The purpose of the first application is secrecy; that of the second two applications is lessening the effect of extraneous noise on the signals.