I made a zone calculation tool which helps on calculating exposure and check needed development compensation. It is for iOS (iPhone), totally free without any ads. It is called "Zone Tool":
https://apps.apple.com/fi/app/zone-tool/id1489637620?l=fi
Hope it helps you, enjoy!
https://apps.apple.com/fi/app/zone-tool/id1489637620?l=fi
Hope it helps you, enjoy!