> I took four zone readings, and went upstairs to fight it out with
> the Texereau book.
>
> About 90 minutes later, I had computed the billion values in his
> spreadsheet like form, and the result is...
Why not use "real" spreadsheet program ? Any will do ... Much less room for errors, much faster, much less tiresome.
>
> The maximum deviation from a parabola is 1/16 wave.
>
> Now, I really don't believe that I just lucked onto getting such a good
> parabola the first time without even trying, so I expect that I dropped
> an order of magnitude here and there, and I have a One-wave mirror or so.
> (An 8 Inch f/7 mirror that is spherical is a One-wave mirror)
This suggests that you might not doing your calculations well. A spherical 8" f/7 has an error of approx 1/4 wave on the surface (or 1/2 wave on the front).
Bratislav