iDoceo will automatically calculate grades and averages for you. The calculator offers an additional method to insert marks and scores to your gradebook. 
Tap on Tools icon (top bar) > Calculator  to start drag&dropping your results. 
 The more conventional numeric keypad
If you configure a column with the Numeric keypad as its editor (video below) you may use a similar method of inserting marks and scores. The main difference with the calculator - besides the actual calculations - is that it may be slightly faster when dropping scores to non-contiguous rows.This is the numeric keypad in action
 
