To: atm{at}shore.net
From: mdholm{at}telerama.com
Reply-To: mdholm{at}telerama.com


Nils Olof took me to task for my comments about PV and RMS on my mirror cell web
site.  Since I wrote that page, I have come around to the RMS way of
thinking. I really should have even then, but my mind was stuck in a rut. 
I do need to rewrite that portion of the page so I stop misleading folks. 
Thanks for reminding me Nils Olof.

There is one way that PV information could be useful in Plop.  If you know
the tested profile of your mirror, and you know the deformations Plop
reports for the cell, you could look to see that the highs and lows of one
are not reinforcing the highs and lows of the other.  For instance, you
wouldn't want to
pair a mirror with a slight turned edge with a cell that produces a low
edge deformation.

The idea of adding the RMS mirror deformation and RMS mirror deformation
using the RMS method of adding works as long as the mirror and cell
deformations are uncorrelated.  It is reasonably possible, since neither
mirror figures or Plop deformation plots are typically entirely random,
that there will be some reinforcement, or cancellation leading to a result
larger or smaller than the RMS calculation would suggest.

Mark Holm
mdholm{at}telerama.com

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