Photometry of rapidly varying stars

I try to do photometry of RU Peg, and I'm not sure I'm doing it right. I have 2x3 images in every session (3 R and 3 I). I have the following questions:

1) Since the magnitude is clearly varying during the session I think it's best to report them separately instead of stacking - the SNR is not too big (~100-200) but I think important information would be lost during stacking. Is that correct?

2) According to the Uncertainty class if I have more than one image, I should report the stddev. of check star of similar magnitude. If I report 3 values for each filter, is it correct if all magnitudes per filter has the same uncertainity, the stddev. of the check star in that filter?

3) As I read it's good practice to transform the magnitudes to a standard magnitude. Since the magnitude is varying during the session the values in (r-i) would be the inst. magnitudes for /different/ real magnitudes. What's the best practice to solve this problem? How to transform the magnitudes of rapidly varying stars?

4) In VPHOT, during Single Image Photometry at the "photometry report" page there is a "Transform" checkbox. If I understand transformations right, I need at least two filters for that. How does that Transform checkbox work with single images?

5) In VPHOT some of the iTelescope.net scopes have their transformation coefficients filled in. Is that information reliable (e.g. regularly refreshed?)

thanks, Peter Bagyinszki (BPEA)