Kye method and metric

This Kye method is something new to me but it makes it easier to subtract. I wonder, does this work with 4 or more digit numbers? I thought that growing up with the metric system made me a master. Well, after not using it for over 30 years, I confused dam with dm........:) Thanks to Dave Santoro and his internet resources we were able to find out the definitions of each and clarify. Ina