I find it interesting that any number of folks on the "members only" listserv of the "Association of Professional Genealogists" are having difficulty with the 1940 census; specifically, the entries where the "M" (for married) has been crossed out and replaced with the number 7.
A quick check of the census procedural history on the IPUMS website explains all this. It means that the person in question claims to be married but that the spouse is not present. The number "7": - it was added by census checkers in Washington. Professionals should know this. This is not rocket science. Bluntly ... look it up!
I blogged about this several weeks ago here: http://mnemosynesmagicmirror.blogspot.com/2012/04/those-pesky-penciled-census-codes-in.html.
Seriously, part of being a professional genealogist is (a.) knowing how to find out what stuff means and (b.) being able to interpret what you find. If either (a.) and/or (b.) is too difficult, you might want to consider doing something else.
