This is a scientific calculator for the iPhone, iPad, and Apple Watch. On the watch, there are three screens. The first has a basic calculator, the second has scientific functions, and the third has trig functions. The app is free, and removing ads costs US$.99.
Free or Paid:
This app is fully accessible on the ipHone and Apple Watch. The developer noted VoiceOver improvements in the most recent update, so this accessibility isn't accidental.