Tangential extracting question

[MichelinMan]

I got my hands on a an electric 4 frame tangential extractor. I read radial is apparently better but hey... this one was free. And this is my first time extracting. I'd like to get advice from those using electric tangentials. How do you know when it's time to flip the frames on the first pass? I was told to extract only half way to prevent frame/comb braking. How do you know when you've reached half way?

[IndianaHoney]

Just turn it on low speed, for about 20 sec, then flip them.