Back in 2015 as the lead designer at mPortal, I had the privilege of working on the a prototype app design for Kastle (yes the same guys they created the office key fob in your pocket). It was a really nice project to think about how a "digital fob" could be used from your mobile device and how other features could make the app "sticky".  Below are screens from the Style and Specs guide for the project.

Before things like Figma, AdobeXD, Sketch or Invision creating a specs guide was a normal deliverable to your development team, thus all the mark-ups and sizing. The spec sheet was a way to hopefully be a guide to the development team on the sizes and layout of each element on the screen.