In this way some characters are coded with one, others with two bytes. The number of codeable characters is finite, the 333 of the repertoire. To make this scheme working a considerable number of letters had to be split into parts. This presented the question what a diacritic is, and what not. The assignment of letters to one or the other category sometimes looks arbitrary.
Programs look to bytes.
The number of bytes in a string is no longer identical to the number of characters. Fields in a record are counted to positions, that is to a multiple of a byte, not to letters that may take one or two, depending on their kind. Thus it cannot be predicted how many characters will fit in a field of a fixed number of positions. Columnwise sorting becomes cumbersome. Because of the problems indicated ISO 6937 never has become accepted in the software-world.