Any steel rules with graduations in 128ths?

[Mini Me]

Blades flex and that is a fundamental problem when using a saw. I have very thin (about 2mm) diamond blade that Leitz make for cutting veneer, melamine etc but try and use that on a mitre cut and it is hopeless. If I want good consistent cuts I have a 5mm thick blade and that never suffers from deflection no matter what it is cutting. For me if it fits the final dimension is a bit irrelevant and a shooting board will always sort it out if needed. 

 

[ChuckM]

True, and that's why getting to know how your saw behaves helps. Even a plane can cut thicker or thinner after each time you re-set the blade. In fact, even with the blade's setting unchanged, the planing can still produce a different result, small it may be. I can "flex" a #4, for example, to make a focus cut with the blade.

 

[Mini Me]

I wonder if two steel rules side by side could be used as a vernier style measurement tool in some fashion to suit your needs.

 

[Packard]

Quite aside from the minimum increment that the human eye can detect (I found 1/2mm listed on google as the minimum—but not source information for that statement), what is the finest line that could be generated on a steel ruler?

Back in 1970, I bought a very pricy slide ruler (Post) that had a white plastic lamination over bamboo body, and a cross hair made from the web of a black widow spider.  Those filaments were finer than anything that could be manufactured at that time (200 to 500 nanometers in diameter).

The 1/128 (approx. 0.008”) size probably exceeds our ability to read the measurement on a ruler, but is a “loose” dimension when using a vernier caliper. 

My conclusion is, use the right tool for the job.  For woodworking, that generally means 1/32”.  Claims to working closer than that are probably delusional.  And for that level of measurement, a steel ruler is fine.  For close work, a vernier caliper or a micrometer.

The problem with vernier calipers is that a 40” one will set you back $500.00 for the bargain basement version and $1,500.00 for a name brand one.