Strehl ratio

I am interested in purching a 18" Starmaster with a Pegasus mirror. The seller sent me a copy of the mirror certificate. No where on the certificate does it show a strehl ratio. It has all the other #'s ie: surface and wavefront P-V error, surface RMS error and wavefront RMS also relative transverse aberration. Is there a way of calculating the Strehl ratio from these #'s. The purpose is for comparison purposes for other Starmasters that are available to me for sale. Any help is greatly appreciated.

Good aproximation for the Strehl ratio is

S~1-39.5w^2

with "w" being the RMS wavefront error.
This comes in a ratio form; to get it in the more usual
percentage form, you need to multiply by 100.

Excuse me that Transverse aberration # is 0.5322

Surface RMS error- 1/96.49
Surface P-V error- 1/29.801
Wavefront P-V error 1/14.9
Wavefront RMS- 1/48.245
Relative tranverse aberration 0.5322

How were these numbers obtained? I can not imagaine that any method had enough precision to allow realistic results to such a number of significant figures.

Hi all --

It's been my impression that Pegasus mirrors rank with the best. Is anyone aware of an inferior Pegasus?
I own an 18" Starmaster with a Pegasus and find its performance superb.

Bob Polcyn