Old thread is past the limit and I have a question.

How is quill stem height measured? I want a new stem with slightly shorter reach but I don't want to accidentally buy one with less vertical extension. I measured it as 160mm top-to-bottom, but are they typically measured some other way? Clamp point to bottom or something? Most common height is 150mm and I've not found a single one with 160 which is why I ask.