This is a tangent from Stewie's "stone flattening" thread, particularly the assertion that ruler-tricking is used as a substitute for flattening the back of an iron. Here's an example of ruler-tricking done as Charlesworth recommends (a quickie snap of the iron from my L-N 8). Note the mirror-finished strip immediately behind the edge:
The back of the iron is dead flat, though not mirror-polished. I worked it to 3 um, or about #4000. The edge was then "ruler-tricked" on 0.5 um diamond paste (#20000-30000) using a 1/4 mm strip of shim stock set about 60 mm back from the edge. The result is a 1/4-deg back bevel, extending a few tenths of an mm back from the edge.
It's probably worth noting that the edge is only recessed from the back by a couple microns at most (~0.5*sin(1/4) millimeters), so the back has to be very flat for this variation of the ruler trick to work. Higher back-bevel angles (from thicker shims or shims positioned closer to the edge) and/or bevels extending further back from the edge will be more tolerant of imprecise flattening.
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