Distance between 2 coordinates

Hello,

So i plot some coordinates in ArcGis, these coordinates are Buoys, and i have the coordinates of where the buoys should be, and where they are in reality. So If i use the rules, i see that there is between 1m and 30m of difference.

Thus i would like to create a new column, or table or xls files with each difference between the original and real position of each buoys.

i have the coordinates in Lat/Long ( after transformation using Eye4software coordinate calculator which is great software for conversion !! )

Can someone have an idea ?

Thank you