If walk through the square in front of the Flatiron Building this week, you'll see an odd sight: Someone with their head strapped into what looks like some sort of medieval brain control device. It's actually just Trevor or Ryan Oakes, artists (and twins) who invented a drawing tool that applies simple mathematics to produce a perfectly scaled drawing.

I caught Trevor drawing yesterday at the Flatiron, and he had already completed a third of the work. Trevor gave me a quick rundown on the machine he and his brother Ryan invented. It's called the concave easel: Invented in 2003, the machine uses a completely original method of projecting an image onto a plane using no external optics.

The easel splits the image you see, overlapping the pen and paper you're using with whatever scene you're sketching. It allows you to essentially just trace the outlines of the real world as your eyes are seeing it. The curved canvas allows your eye to have an exact match between the canvas and the way you interpret your surroundings.

This specific easel is the third iteration of the brothers' invention. Trevor explained how the first two were all made with flimsy wire and wood frames. It could take a few hours to set up and take down.

The brothers have done a total of 25 drawing with the device so far. A single drawing usually takes around three days of work, but end up overall consuming a month of the brothers' time. Trevor and Ryan co-direct the sketches by picking a location and deciding what type of line work will be used. Then, they go on location and construct the piece. Trevor has ended up doing more of the sketching since he's had more practice with it, though sometimes they will pass the pen back and forth.

The two panels that had been completed before I got there, yesterday, took a day and a half to drawâ€”and the rest of the panels Trevor guesses will take him another week and a half. If you happen to be around the flatiron building around midday this week, be sure to keep an eye out for Trevor, Ryan, and their concave easel.

The brothers have 12 years of artwork on display at the Museum of Mathematics (MoMath) currently on display for those who are interested.