When typing in programs from a book or magazine, the best number system to use is hexadecimal (base 16) because you only have to worry about 16 different keys (0-9 + A-F) and a 2-byte checksum so you can correct mistakes, and hex can easily be converted to binary code by translating each byte into binary. It also uses less space than decimal8). The octal (base 8 system) is also a good system to use because you only have to worry about using 8 different keys (0-7), and each byte can be converted to a 3-bit binary number. The worst system to use is BASIC, because you have to worry about 10 different number keys and the entire 26-letter alphabet and special characters (about 20), bringing the total to 56 different keys. You should definitely use a checksum if you're typing in a BASIC program. The Commodore 64 could use a program called MLX which allowed computer users to type in 2 hexadecimal digits at a time, followed by a 2-digit checksum at the end of each line so the user could correct mistakes.