org-calc-default-modes

org-calc-default-modes is a variable defined in `org-table.el'.
Its value is

(calc-internal-prec 12 calc-float-format
		    (float 8)
		    calc-angle-mode deg calc-prefer-frac nil calc-symbolic-mode nil calc-date-format
		    (YYYY "-" MM "-" DD " " Www
			  (" " hh ":" mm))
		    calc-display-working-message t)

Documentation:
List with Calc mode settings for use in `calc-eval' for table formulas.
The list must contain alternating symbols (Calc modes variables and values).
Don't remove any of the default settings, just change the values. Org-mode
relies on the variables to be present in the list.

You can customize this variable.