Strehl or Wavefront error...which to consider?

I'll soon be the owner of a mak-newt scope, and i'll be receiving a cert. of optical quality. The certificate specifies a wavefront error of 1/7.8 wave p-v @555 nm, while the strehl ratio of the system is 97.5%. According to the following: http://www.rfroyce.com/standards.htm
a 97.5% strehl ratio corresponds to a wavefront error considerably lower than 1/7.8 wave (more around 1/11 wave). So, is it possible that the stated wavefront in the certificate is inacurate, or misleading as to the real quality of the optics? Also, which standard should I place more weight on as a measure of optical quality for my scope, wavefront or strehl? Thanks.

IMHO Strehl ratio is a better indicator of optical quality.
It is measuring what you really want to know about --
which is the percentage of light going into the
Airy disk.

Peak to valley is a useful indicator, but what it does
not tell you, is the fraction of the optic at that
maximum error. If a large area of the optic were
at the maximum error -- say if it is due to spherical
error -- then there will be a large impact on image
quality. But if there is only a tiny area involved
-- say a central zone or bump (or even spec of dirt)
-- there might be almost no impact on the images.

It is not possible to relate bewteen P-V and Strehl
without making some assumption about the distribution
of errors on the surface. For the example given by
Royce they are assuming a spherical error, which
will involve a large area. The fact that your Strehl
implies 1/11 wave (spherical assumed) and the measured
P-V is 1/7.8 just means that you've got a small area
at the maximum error (this is good). It likely means
the errant region is a narrow zone or edge effect.

It depends on how the numbers are determined. If they're determined by interferometry, then they're probably more accurate than if they're derived from Foucault measurements. In the former case, I would trust the Strehl ratio more. In the latter, I'd trust the P-V more.

Truth be told, if the mirror is smooth, has no sharp breaks, and a good edge, then even a 1/7.8 (let's say 1/8) wave P-V wavefront is very, very good. You may see a difference with a better mirror when doing the star test (virtually no mirrors "pass" the star test 100%), but at focus it's highly unlikely that you'll see any difference at all.

My $.02

Doug