I'm writing my thesis now, but I wonder which part they usually focus on? Do they read the results and discussion chapters more careful than the things before them? Will they read my experimental methods carefully? I mean, do I have to dig out every detail of my experiments and write them down? Is it worth it? I hope I don't need to spend too much time writing every detail. If they don't read it carefully, then I shouldn't waste my time write a very detailed thesis.

Not sure how helpful this is but I believe 'How to Examine a Thesis' by Lynne Pearce is a well-recommended book to help PhD students understand how examiners examine, if you have time to read it...

I also saw an interesting twitter thread today by a thesis examiner @ VikiLovesFACS. She said she looks up papers and methods she's unfamiliar with (suggesting she does read carefully). But she also says the time limits of a viva mean she can only bring up a third to a half of the points she'd like to discuss (suggesting you can get away with things, though ofc you can't know in advance which things the examiner will want to discuss in detail).

My gut feeling is to write as detailed as you can manage, while staying sane :)

Thanks cucaracha. That's helpful.
I think it's difficult for me to stay sane if I need to find out every supplier's name for each sample we've bought and to draw a picture of the experimental setup...

I think it varies a lot on the examiner but I agree with cucaracha. You only need to right enough so that it looks right. The detail orientated examiners will be picking regardless of how much detail you write. Though you can probably do reconnaissance on your examiners and find out what they are like. I know that my first choice external examiner does not understand the methodology and is useless at the practical side of doing experiments. So if you know who your examiners are you might be able to write around them.

Also, you don't need to list every supplier unless the choice of supplier affects the results. I was told if three or more papers have used a similar method, you don't need to explain the experimental method in absolute detail.

I asked my external about this at the end of my viva.
He said he starts with the reference section. He knows who I should be referencing because he knows the general field and he's looking to check I've not missed anyone important. If he sees all the major players being referenced, he can be confident that I've done my homework.