HELP - Suggestions for Double Entry techniques for Data Entry

I have a large data entry system that needs a method of doing double
entry to eliminate a lot of user error.  What I have now is a system
that  when ever the user changes a datafield, if double entry is on, I
do a query on that one field and then compare the values.  I have cached
updates turned on so the query represents the initial value and the new
typed value is compared against that.

This works alright but I would like to hide all the data from the user
so they must actually look at the original to do the double entry...

Is there anyone who has implemented such a system and how did you do
it.  I do have one other exception... i don't want to have to double
enter memo fields.