Need help with induced astigmatism

[Maksymilian]

Hello Everyone :)
This is my first post:)
I've got problem to resovle which is very important for me.
As we know if lens will be tilt, it's power will change. We can calculate it in this way:
"New shere power= sphere[1+(sin a)^2/2n]"
where n is refractive index, a- tilt of the lens (pantoscopic or face form angel).
And we also can calculate cylinder power induce by this tilt:
"cyl=(new sphere)(tan a)^2"
My question:
if I'll calculate two cylinder error power in ax 90 degrees and 180 (induce by PT and FFA),and I have prescription for eg. -4.00 -1.00 x 45, how can I know what is real power in prescription ax?
I'll be grateful for Your help:)
Above formulas were found in "Systems for Opthalmic Dispensing".
P.S.
Please forfive me my style but I haven't use English for a long time:bbg:

[lensgrinder]

Follow this link to OptiCampus where there are optical calculators. If you are asking what the Rx will be if you put an Rx in a frame with X tilt and Y wrap then the math is pretty long, but here is a great thread about the subject. There is a great article called Oblique Central Refraction by Michael Keating.