For technical documents, I definitely recommend getting a tablet with 4:3 aspect ratio instead of the more geared towards video 16:10 or 16:9.
Some pics of my iPads taken using an iPhone 7. Note, the images are HUGE.
Image #1: Pro 12.9 in landscape double page
Image #2: Pro 12.9 in portrait single page
Image #3: Pro 12.9 and iPad 9.7 in portrait single page
Image #4: iPad 9.7 in portrait single page