Dimension an angle at drawing mode without a horizontal line as reference

How to dimension an angle in drawing mode without a horizontal line as reference?

Imagine if I have an inclined line only (not a second line). At SolidWorks, I click the line and click at the end point of this line and click at one of 4 options of arrows (2 horizontals and 2 verticals) as reference to insert an angle. Can you see? I didn´t need a sencond line to show an angle of one line. How can I do it with Onshape?

NOTE: at Part Mode, I use an plane as reference.

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