With the Miira View Frame you can accurately observe the many aspects of linear perspective.
The user can do this:
While looking at your subject, hold up the View Frame at arm’s length and perpendicular to your line of sight. Place a guide into the track and with single vision (close one eye), align the guide with a linear edge on the subject. The guides will pivot and slide easily on the track and once you have them in place, they will be fixed until you move them again. Now, fix another guide to align with another edge, and so on. As you place the guides onto the frame to record what you see you will begin to learn and even be surprised at how the eye observes the natural world!
Once you've seen and registered the truth of the scene through the View Frame, you can easily and accurately record one, two and three-point perspective.
Now that you have registered the guides onto the View Frame and have learned about the scene you are trying to render, notice the degree of slope of each guide you’ve placed onto the frame as they relate to each other and to the edges of the frame. Lightly sketch what is registered on the frame onto your surface - just rough it in. Now, step away from your easel, hold up your Miira View Frame, close one eye again and look through the frame to compare what you have registered on the tool with what you have sketched in. Be sure not to move the guides yet. They will help you to see any problems that exist with your sketch.
In fact, you will instantly see the correctness or the inaccuracy of what you've drawn. Now you will know what to do to fix the problem or you will be satisfied that you got it right!