The difference of the two has been explained in another post:

"A note for those not familiar with rotation options. Geographic rotation establishes due north as angle 0 and degrees above 0 cause a clockwise rotation so that due east is 90, due south is 180 and due west is 270. It's rules are designed to operate like a clock. An Arithmetic rotation follows Cartesian graphing rules and is what mathematicians use. It establishes the X axis in the positive direction (X = +, Y = 0) or due east in compass directions as 0 and degrees above 0 cause a counterclockwise rotation. In an arithmetic system due north is 90 degrees (X = 0, Y = +), due west is 180 degrees (X = -, Y = 0), and due south is 270 degrees (X = 0, Y = -)."

The concept is clear to me... but how can I caculate one from the other? As I have aritmetic direction in my data, but I need them in geographic degree.

Thank you! Frauke

Have a look here, quite old:

Point Rotation