implementation-notes.md is generally very good. A few suggestions for improvements:
[x] Use uppercase for screen and scene names, because that's how they are labeled. And you've used uppercase in model.md. E.g. "...the Explore screen..." versus "...the explore screen..."
[x] Provide links to the .js files for sim-specific classes, so the reader can easily navigate to the code.
[x] Property (uppercase) and property (lowercase) are totally different things. You are using the latter where you should be using the former.
[x] Where "number line" is used as an adjective, it is a component adjective, and should be hyphenated. E.g. "The number line is..." vs "The number-line features are..."
I made several of these improvements in the above commit, checked off in the checklist above. I'll leave it up to you to decide whether to add links to .js files.
Related to code review, https://github.com/phetsims/number-line-distance/issues/35
implementation-notes.md is generally very good. A few suggestions for improvements: