What is the crowd's opinion of Adobe Photoshop Sketch?

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You should maybe give Concepts a spin: https://concepts.tophatch.com They have a precision mode which provides a few different customizable guides.

Edit: Also, if I remember correctly, Adobe Sketch has a few different built in guides, too (French curves and the like), as well as a perspective grid mode. Fewer options for precision and exact measurement, but also free. http://www.adobe.com/products/sketch.html