Anyone interested in magnetic field & "weakening".
Buy yourself a good compass - $30-$40 - used quality ones from the 80s are pretty good
Look at how sensitive they are to metal and other modern stuff any wires anything. If put it above a screw in your desk, it is useless
Looks to me there may be another reason for the apparent field weakening, all the EMF junk and even just the amount of steel produced and used in our cities
To get real measurement of field, may need to do it at 30K feet or above