Using "dp" and "sp" in drawing

I'm trying to make a little app that has a little meter in it (think like a speedometer). Well, for the pointer (you know what I'm tal开发者_如何转开发king about), I want to make it an 1/8th of an inch thick, independent of the display size.

How would I go about doing this?

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Use in (inches) as your unit instead.