If you want to measure the position of graphic elements. You can try ads called xscope. A version of the trail can be downloaded from the official website. This is the best tool I've ever seen for measuring distance, color (for example, it can copy color measured directly in the [UIColor ...] format), etc. If you want something free, I would like to recommend markman, which is Chinese software, it is built on black air. All elements / buttons are graphic, so you do not need to read Chinese to use it.
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