I have played around with this method before but its very messy and by the way you described it would have problems. If i had a list of 5 things, and I moved the #2 in between #4 and #5. Then subtracted the ones below by 1 then 4 would be #3, 3 would be #2 and 1 would be -1. Theres usually issues like that making it quite complicated, the decimals seem to work better considering there will be lots of exceptions to your rule.