NavList:

When performing calculations involving degrees and minutes, I much prefer converting the minutes to degrees, proceeding with the additions and subtractions, and then converting the decimal degrees back to minutes.  

There may be some statistical reason for not doing it that way; or, is the practice perfectly acceptable.   

There are those professionals who teach navigation that insist upon working only with degrees and minutes, unless it's necessary to use decimal degrees for calculator entry in which case they carry the decimal out to the fifth place.  

What are the rules, if any, that make the degree/minute conversions unacceptable; and, if there are prohibitions against the practice, is there anything one can do in the process that will statistically justify the conversions?   

Steve OCBC