Outside References
According to Christopher Bidmead, the Logopolitans employ a hexadecimal, or base-16, numerical system, a real system commonly used in computer programming. When Adric and the Monitor read strings of numbers and letters, the letters are actually the numbers between 10 and 15, expressed as single digits.
The Police Box that the Doctor materialises the TARDIS around in Part One was intended to be the one located at the Barnet bypass, which at the time was one of the last police boxes in the Metropolitan Police District still in its original location, though it had ceased functioning in the 1970s. It was removed in 1981 prior to the filming of this story.
Read more about this topic: Logopolis