About
You can measure with:
- the Measure tool (M).
- Measure Path extension that will measure the length of an arbitrary path.
You can set the width and height of an object in the selector control bar.
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Angle
The angle is measured by default from 3 o'clock origin counterclockwise (the mathematical convention), but in Preferences you can switch this to using compass-like measurement (from 12 o'clock, clockwise).
Tool
The measure tool. Just click on a start point, hold the mouse button, and drag to the desired end point. Just as you would use a measurement tape. Snap is working