How to draw rullar in iphone sdk?

Hi I w开发者_运维问答ant to make rullar in iphone. Que: How to draw lines through UILabel in scrollView 1 inch. or 1 cm. apart from each other. I know there are 163 pixels per inch(ppi). in 480-by-320-pixel. But I am not sure about all version of iPhone .

Does the size of pixels are same for all its model???

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Drawing in iOS uses point values rather than pixels; in a retina display there are four pixels (2x2) in a point and in a non-retina display there is one. The screen sizes are the same (with the obvious exception of the iPads). If you draw a line from (0,0) to (0,100) it will be the same length on the screen of the iPhone 4 and iPhone 3GS.