From the beginning we wanted to make our math explanations as accessible as possible. It turns out that it's pretty challenging to preserve the math in a form readable by screen-readers. Thanks to heroic efforts by Make's production team,  there is an epub3 version of Make:Calculus at https://www.makershed.com/products/make-calculus-pdf.  The Thorium epub3 reader is recommended. (The link gives you a pdf for visual reading, too.) Of course if you like paper, that's available at https://www.makershed.com/products/make-calculus-print and the usual other retailers.