The formula for the calculator: x=y/0.4
There are a total of five screens, most of them static text, as follows:
1. Disclaimer - button tap to continue
2. Intro Screen - option to continue, choice of two destination screens (calibrate screen or instructions screen)
3. Calibrate Screen - entry of one data point (y).
4. Explain results - showing (x).
5. Instructions - static text
EDIT: Additional screen and function - save measurements of (y), show list of previous, with best/worst/average (y).
This is an iOS / iPhone app. If you can do Android also, please mention in your bid.