I can not seem to find the information on using a tight wire for checking strangeness. you put your straight edge on a flat surface. place a piece of round stock, like a gauge pins with the same diameter, on top of each end of the straight edge. Then use a piece of .006" music wire (not sure on the dia.).one end of the wire is attached to the table then placed over the first pin down to the top of the other pin and wire is draped over the edge of the table with a 16 lbs. weight attached (not sure on the weight). this will preload the music wire and the sag of the wire will be near zero in 2 ft, the length of your straight edge. you can use feeler gauge stock, or what ever method you chose measure the distance from the wire to the straight edge. there are tables that show the sag of the wire in lengths of 30 ft if I remember right. this method will definitely check your straight edge. gauge pins have to be the same dimeter, wire has to have the same dia. the full length of the test length.
Corrections to the above diameters and weights........
See
Forrest, I found it. Wire sag table.
.016 dia piano wire with 30lb weight
lenth of wire, sag and distance from end
4ft .001 at 2'
8ft .001 at 2',.002 at 4'
12ft .002 at 2',.004 at 4',.005 at 6'
16ft .003 at 2',.006 at 4',.007 at 6',.008 at 8'
20ft .004 at 2',.008 at 4',.011 at 6',.012 at 8',.013 at 10'
24ft .006 at 2',.010 at 4',.014 at 6',.017 at 8ft,.019 at 10ft,.020 at 12'
28ft .007 at 2',.013 at 4',.017 at 6ft,.022 at 8ft,.024 at 10ft,.025 at 12ft,.026 at 14'
32ft .008 at 2',.015 at 4',.021 at 6',.026 at 8',.030 at 10',.033 at 12',.034 at 14',.035 at 16'
36ft .009 at 2',.017 at 4',.024 at 6',.030 at 8',.035 at 10',.039 at 12',.042 at 14',.043 at 16',.044 at 18'
40ft .010 at 2',.020 at 4',.028 at 6',.035 at 8',.040 at 10',.046 at 12',.050 at 14',.052 at 16',.053 at 18',.054 at 20'
I hope this looks like something when I post it. Here goes.