Map zoom in the Faims app using the Nutiteq library appears to scale in the following way: 

• Zoom set to 17.0, Map scale is 200.0m with full bar
• Zoom set to 15.0, Map scale is 1.0 km
• Zoom set to 14.0, Map scale is 2.0 km with full bar
• Zoom set to 13.0, Map scale is 2.0 km with half bar
• Zoom set to 12.0, Map scale is 5.0 km with half bar
• Zoom set to 12.0, Map scale is 10.0 km with half bar
• Zoom set to 10.0, Map scale is 20.0 km with half bar