But anyone who has seen me work knows I also use mirrors. Instead of backing up from the piece all the time, I use a hand mirror to view the work at double-arm distance. In addition, the mirror also flips the piece, making any mistakes instantly visible. You can see if the composition is falling off one corner, if a piece of architecture is asymmetrical, or if the impact of the color needs fixing.
Usually, I have been looking at the painting for a long time, so to see its flipped version makes my mistakes immediately clear. Since I work alone, it's the only way I have found to get fresh eyes on the piece without consulting other artists.
For example, here's my 2008 painting, Red.
Everything looks normal. But view it flipped: