CTFFIND3 and SPIDER :astigmatism and astigmatism angle and tilt angle

Hi
my questions are regarding conversion between the values from CTFFIND to the ones that I should use for TF C (CTF correction)in Spider,

first, if I understand correctly I should use the average of DFM1 and DFM2 as the defocus value

but then,
should I use the value of the following difference as astigmatism?

(DFM2 - DFM1)

or should I use (DFM2 - average)

according to TF C command in SPIDER the astigmatism is :
the defocus range due to axial astigmatism. In the example the value given indicates a defocus range of +/- 400A around the nominal value as the azimuth is varied.

The last sentence sound to me as the difference between the any extreme and the average ("nominal")

I am confused because there is another page in spider where the astigmatism definition reads: magnitude: the difference between the highest and lowest defocus.

Do you know either which one is correct? or how can I tested it?

Regarding the astigmatism angle

If (DFM1 - DFM2) > 0 , the angle is angle_spider = angle_ctffind + 45.0
If (DFM1 - DFM2) < 0 , the angle is angle_spider = angle_ctffind + 135.0

is that the correct conversion?

Finally what is the correction between the tilt angle from CTFTILT and the one used in SPIDER?

thanks a lot in advance,