The easiest way to do it is to download Inkscape, then print the mask image to get one half, slide it to the left to get the other half, trim each of the halves, and paste them together.

You might have to do each quarter separately, depending on the size of your scope, the outer edge thickness you use, and the size of your paper. Under the print options, putting in a "Center line color" of red or black can help you line up the halves/quarters.

I keep saying I'm going to add an option to produce multiple files, but I haven't gotten to it. I'm off for almost two weeks for the holidays, so I might spend some time upgrading the generator.

Hopefully, John W (or someone else who actually knows about/understands the physics) can weigh in on this, but I think this is in reference to the wave harmonics that create the interference patterns we see, that line up so pretty when we're in focus. The 3rd order is what makes the "divide the Bahtinov factor by three" thing still produce a workable mask/pattern.

David