In article , Dave Baker says...

By lapping 3 plates against each other with grinding paste until all three are
flat. The same way as reference plates are made now. The ancients could make a
plate as flat as we can now. The technique requires no special technology.

Not strictly true, Dave. Read the description about flat
surface generation in Moore's book, they go into considerable
detail on this.

1) they use cast iron plates, specially ribbed and supported.

2) the square plates are spotted against each other with a
marking medium, and are hand scraped to each other.

3) the exact sequence of operations matters, and there is 90
degree rotation included between each cycle. This prevents
a saddle error from developing.

4) once the plates are spotted and hand scraped as well as
possible, each plate is then futher corrected using several
additional steps, to get down to roughly one micron flatness
level. Unless one includes these steps, they say that ten
or so microns is all that can be achieved.

Probably the *most* important technologies that we have, that
were not available to the 'ancients' are a) more accurate
metrology, and b) temperature controlled environments for
doing the measuring in. The second is probably the most
important.

Moore's book give considerable engineering detail about what
is now pretty trivial stuff, but when the book was written is
was state of the art, he talks about feedback loop control
of HVAC systems in their plant.

Jim

==================================================
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================