Numbers version 5.3(5989). How to Calculate Duration by comparing two cells formatted as datetime? Column A has been formatted in the “datetime” format. Date and time from my glucose meter were entered into Column A and displays as in the default option I selected. Column D is the glucose readings and is not an issue in this question. (Datetime format displays as “1/5/2019 1805”). Also Column A has been sorted in ascending order and verified. 
Column B is formatted as “duration”. 
What is the function (formula) to compute the interval between successive dates &amp; times in Column A?
Every attempt I have made results in “number was expected”.
You just need to subtract the later from the former.

ie: B2-B1