how do midwives know how dilated you are?

[ThatllDoPig]

Do they measure their finger width when they are training?
Just wondering, to be that specific about 7, 8 or 10 cm, without a ruler?!
Anyone know?

No idea! Mine said I was "about 6 cm" that it "could be quick from here, around an hour", she went out of the room and DD's head popped out. She later confessed that she had mistook the head for the cervix? (or something like that)

They use 2 fingers, insert them into the vagina and feel around the cervix. They then estimate the distance between the 2 fingers. Does that make sense? If you insert 2 fingers into a cup and stretch them so that they touch two sides of the cup, you can roughly guess how wide the diameter of the cup is. It just takes practise to estimate.