In iOS 9.3.1 the were advanced settings for dates, times, and numbers in Settings > General > Language & Region > Region Formats, just under Calendar. You could use these to set format for dates etc. different from your device default language or region.
Although the User Guide for iPhone or iPad for iOS 10 states it should be still there - it is not!!, Instead, a temperature unit selection appears under calendar.
It should be back!! Very important!!
