You say "calculation" and "look ups". Look up is what you are looking for...rather than constantly referencing the other table with real time updates, they grab the current value and shove it in your field...not to change if you now change the referenced field.
Learn about lookups...they are the tool you seem to be looking for. Then do your totalling claculations based on those looked up values.
Thanks so much for the reply, Lookups are just what I needed, easy solution too.