Thanks all for the help. The final solution is slightly more complex but the responses gave me a really good steer.  Essentially it turns out that a (small) number of records have more than one byte so using '00'x as a delimiter risked cutting off some values where the final character was 0.  So I substituted this with '002'x to generate the string containing true values then created an array to loop through this taking every odd character to create the final string to translate to a number.  Not very elegant but works and can also be applied to other fields where I have the same issue. So much for hoping there was a simple format to do this! ... View more